El Beast - Initial design phase, comments and critique welcomed!

yes fair enough, I'm going with a single rail each side.

I like the look of the misumi milled profile - they have it in the 45x90 size i was originally planning. Just need to figure out how to actually buy the stuff and how much it is.

Edit - Father in Law is happy to get it through his company, now just a question of how much dolla!

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Originally Posted by Zeeflyboy

yes fair enough, I'm going with a single rail each side.

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It is a good decision. Now just turn them 90 degrees and place them under the table. Squaring will be a problem if you are not doing that. You would also get a more rigid machine if the rails are mounted horizontally.

Why do you think it would it be more rigid?

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(3) High rigidity in all four directions
Because of the four-row design, the HG series linear guideway has equal load ratings in the radial, reverse radial and lateral directions. Furthermore, the circular-arc groove provides a wide-contact width between the balls and the groove raceway allowing large permissible loads and high rigidity

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Personally I think the machine as a whole will be more rigid with the current setup as it allows me to bolt the frame and frame supports to the tool bed for added frame rigidity while keeping the unsupported gantry arm to the minimum length. If I flip the supports 90 degrees and set them up like my current machine then I have an unsupported bed that will flex, and I can't put the cross supports in as they would then interfere with the ball screws... unless I underslung them which would be a mounting nightmare.

Just out of interest, 50x100 GFS (high rigidity version, 6.8kg/m) milled profile works out to around £70 per metre before tax.

Given I only need 2 metres of it that's not too bad really for a milled mounting surface I think... might be the way forward.

Quote:

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Originally Posted by Zeeflyboy

Why do you think it would it be more rigid?





Personally I think the machine as a whole will be more rigid with the current setup as it allows me to bolt the frame and frame supports to the tool bed for added frame rigidity while keeping the unsupported gantry arm to the minimum length. If I flip the supports 90 degrees and set them up like my current machine then I have an unsupported bed that will flex, and I can't put the cross supports in as they would then interfere with the ball screws... unless I underslung them which would be a mounting nightmare.

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Yes, it would be. But there is the challenge to align all.

The only way to align that easy and properly 100% is to rest all frame on flat surface and lift rails on paralel blocks same size and then tighten. But i assume you dont have that flat surface. So you may have to think of sth else. What i am saying here is that a design is as good as you know all steps, to finishthe machine. To figure the details meanwhile you are building it=wasted money and time

Thought we already mentioned that the rails would be aligned to the ecocast ground bed plate?

I'll be using Thorlabs precision corner brackets for frame squareness (combined with the ecocast end plates and milled extrusion).

Does that not cover the alignment issues, especially given the relatively small size of the machine?

They will be aligned left-right, not up-down , plus have to be straight up down, not wavy, same for left right, but as you said that will not be a problem as eco cast plate. 3d, means there are 3 directions that things have to be on plane

No, they would be aligned in the vertical plane too... ecocast bed plate could be fastened to the top and then I would insert a shim of 2.5mm between carriage and bed with the carriage at one end, clamp it in place and tighten end screw. Move carriage to other end, insert same shim again and clamp. Tighten that end screw... If required you could repeat that at several points along the length.

Repeat on the other side and both rails are aligned vertically using the eco cast bed plate as a reference.

The parallelism and squareness of the Y-rails would be taken care of to acceptable tolerances by the captive ecocast end plates, milled extrusions and thorlabs corner brackets, while the vertical alignment (both in X axis rotation and Z plane height) would be done in reference to an ecocast bed plate.

What am I missing? In my head that ends up with the rails fully aligned in all axis to within the tolerance of the milled surfaces which should be sufficient for a pretty accurate machine all said and done.

Seems 100% ok what you are saying. Thats very similar to the way i thought it could be done.

Ok great, thanks - glad you agree with my thinking then!

I've just done a mass analysis on the finished machine and its coming in at just shy of 190kg... I know mass is but one suggestion of rigidity but that's not far off 3 times the mass of my current machine.

I've also taken the opportunity to change to a HGR25 rail and HGR25HA carriages on the Y-axis since there is more space now.

Had a quote back for all motion parts, it was pretty reasonable for ground screws and HIWIN rails. Think I'm good to pull the trigger on those parts?


http://i.imgur.com/kJvfLRJ.png

Few comments:
- I do not understand why you are using AL profiles and AL plates, check stiffness...
- design of lower (x) rails is .... You need to grind both surfaces to get perfect parallelism, otherwise will linear bearings feel the load caused by angular displacement of both rails , put them on the top of the table, in same plane - much easier for DIY,
- design of gantry (y) - it must be closed beam - it has no sense to do a "nice look" without functionality,
- side brackets, what is the method for setting the "true" right angles? Do you expect that everything will be machined within few microns? , y length tolerance stack is problematic anyway
- foots: do you expect that desktop is planar?, machine must be stable, it looks nice, but

Before design set the requirements i.e.
- max work space
- max space for machine
- max tooling dia
- material of machining
- define what you wish to do ( mirror surfaces, engraving...)

and the start with design.

regards

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Originally Posted by fifa

Few comments:
- I do not understand why you are using AL profiles and AL plates, check stiffness...

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Why alu profile, because it is available cut to length at sizes larger than I can handle myself with decent precision and also with ground surfaces from misumi. GFS (high rigidity) profiles are being used, they have substantially more mass than normal profiles.

Why alu plate, because I can process aluminium plate myself and I can buy it in ecocast form with a high flatness tolerance, again readily available. If I pay for every part of this machine to be made up in steel to high tolerances by someone else then I will not be able to afford it, even if the material itself is cheaper... which i'm not sure it is when you start talking about milled tooling plate.

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- design of lower (x) rails is .... You need to grind both surfaces to get perfect parallelism, otherwise will linear bearings feel the load caused by angular displacement of both rails , put them on the top of the table, in same plane - much easier for DIY,

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Both surfaces are ground...

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- design of gantry (y) - it must be closed beam - it has no sense to do a "nice look" without functionality,

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I don't understand what you mean here.

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- side brackets, what is the method for setting the "true" right angles? Do you expect that everything will be machined within few microns? , y length tolerance stack is problematic anyway

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That little mounting plate at the bottom of each side has an eccentric nut on one end and a DIN shoulder bolt at the other, which will allow the entire gantry to be trammed fore/aft, while the side arms and mount plates are both made from eco-cast plate which will have to sit flat to each other when bolted together. Further adjustment is available on the spindle mount for tramming left/right.

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- foots: do you expect that desktop is planar?, machine must be stable,

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On a machine this small I think adjustable feet are more trouble than it's worth. Better just to make sure you have a flat level surface for it to sit on... depending on what I can find I will either sit it on a granite block or pour a self levelling base block for it which will form the bottom of my enclosure.

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Before design set the requirements i.e.
- max work space
- max space for machine
- max tooling dia
- material of machining
- define what you wish to do ( mirror surfaces, engraving...)

and the start with design.

regards

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My design requirements were of course set out before I started to design it... the majority of what you list there was mentioned in the very first post. I'm not sure how you can even start designing a machine without knowing what you want it to do...


Thank you for the feedback but I do think there is a danger sometimes of losing sight of reality on this forum. For what is ultimately a small hobby desktop machine the rigidity of a 50x100mm GFS extrusion and 20/25mm alu plate is hardly going to be the limiting factor... This machine will be an order of magnitude more rigid and precise than my current one while expanding the work area, which is really all I'm after.

A few frame details... made up using 50x100 and 50x50 milled profile now.

Bottom screw nut mounting plate will probably become a single piece once I have a machine large enough to make it.

http://i.imgur.com/MZYunIM.png

http://i.imgur.com/M6oqBs5.png


Gantry fore/aft tramming adjustment (both sides)... undecided whether to go this way or just rely on shimming for this bit.

http://i.imgur.com/VYdSLoU.png

Sorry I am not native English speaker, therefore I can be easily misunderstood.

X rails: pre-machining rails do not count due:
- rails must be parallel - your design is frame from 4 profiles. Forget on straightness (you are assuming this will help with using expensive profiles.) think about other two elements which are connecting both profiles.
You have 2 plates - potentially nonparallel, two profiles Mitsumi + two profiles catted and machined by... as I said check the stiffens of the bearing, lets assume the total error of non-parallelism is 100 microns, and that half of this error must be compensated by bearings, the other half by brackets. This means 25 microns per bearing - now check the stiffness and you will see the load which is in the "system". If you wish to remove error, you need to do machining in the assembled condition...

Check the I (Area moment of Inertia) of profile and plate, most likely 25 mm thick plate is stiffer than 50 mm profile or it is close to it. And whatever will you do: If the profile and plate are not planar, when they will be assembled the result will be non-straightness of the rail "bed" surface.

Y gantry: problem is torsional load not the bending - check the I and calculate displacement applying 100 N force at the end of the tool
The second problem is: Y gantry length must meet X rail width - within micron range otherwise you are facing with additional load to the X bearings... Not mentioned that both side surfaces must be parallel, - if not additional load on X bearings again

Regarding the idea of setting the true angles with bolt - by definition this means you are incorporating elasticity in relative stiff system. Means also you have nice oscillation.

You are right system is relatively rigid. I am escalating problems caused G&T and consequences of those.

regards

regards


,

Well I think that compared to my machine, which is welded steel frame with a bit of epoxy for levelling the rails and some 20mm tooling plate for the gantry, this is far more of an engineered and well thought out solution. Thought has gone into how to assemble the machine and the OP is very realistic with respect to the area they want and what they want the machine to do.

I think gents that everyone is getting a little too nit picky (which, don't get me wrong, can be a good thing) and getting a little bit too bogged down in ultra precision engineering and forgetting that this is a hobby machine..............there is nothing here in this design of machine which couldn't be sorted with the help from a few beers an assortment of shims and a bloody big hammer :whistle: :biggrin:

Absolutely agree. There may be some minor adjustment needed at the end but there would be with ANY machine (except possibly a Datron). It looks more well planned than most other DIY machines that have turned out just fine.
ZeeFlyBoy your skills with Fusion 360 are incredible.

Thank you chaps! Neil I think you summed up my thoughts quite eloquently - especially the beer and hammer part lol.

I am of course after critique, it was the main purpose of sharing this design before starting to build it rather than vice versa - and I am extremely glad I did.

The complete change to the Z-Axis for example is not something I would have thought of but I can definitely see the benefits... but ultimately yes, one needs to keep sight of the fact that this is a hobby machine to go in the Man Cave, not an industrial interferometer calibrated machine.

I am confident that the design as it now stands will fall within the alignment error ability of the linear rail carriages, and with some tweaking I think I can get probably get it to within my ability to accurately measure.

Jumper - Thanks but I'm still just an amateur with Fusion, but I do find it refreshingly easy to use for the most part!

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Originally Posted by fifa

Sorry I am not native English speaker, therefore I can be easily misunderstood.

X rails: pre-machining rails do not count due:
- rails must be parallel - your design is frame from 4 profiles. Forget on straightness (you are assuming this will help with using expensive profiles.) think about other two elements which are connecting both profiles.
You have 2 plates - potentially nonparallel, two profiles Mitsumi + two profiles catted and machined by... as I said check the stiffens of the bearing, lets assume the total error of non-parallelism is 100 microns, and that half of this error must be compensated by bearings, the other half by brackets. This means 25 microns per bearing - now check the stiffness and you will see the load which is in the "system". If you wish to remove error, you need to do machining in the assembled condition...

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All profiles are going to be from the same place (mitsumi now, given I want the milled stuff) actually, given that they almost certainly should be cutting the bracing profiles one after the other without re-positioning the cutting gate they should be very, very close.

They can always be massaged with my current machine which will happily repeat to substantially better than your stated 100 micron example (as confirmed by some fairly expensive glass scales mounted to both X and Y axis). It should be fairly easy to get them to within 10's of microns rather than 100's...

Quote:

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Check the I (Area moment of Inertia) of profile and plate, most likely 25 mm thick plate is stiffer than 50 mm profile or it is close to it. And whatever will you do: If the profile and plate are not planar, when they will be assembled the result will be non-straightness of the rail "bed" surface.

Y gantry: problem is torsional load not the bending - check the I and calculate displacement applying 100 N force at the end of the tool

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This is a bit beyond me, I have never used any simulation software and not sure where to start.

I'm simply going on the basis that common sense Garden Shed engineering tells me a combined total of 32mm of solid aluminium plate and 40mm of heavy profile that makes up the gantry cross section is overkill for a 550mm span gantry on a relatively light duty table top machine. Certainly it is at least as beefy as most DIY machines of that scale that I have seen.

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The second problem is: Y gantry length must meet X rail width - within micron range otherwise you are facing with additional load to the X bearings... Not mentioned that both side surfaces must be parallel, - if not additional load on X bearings again

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I don't really see this being an issue as long as it's longer rather than shorter. All it requires is to try inserting a shim brass sheet of various thicknesses between the gantry arm and mounting plate until you find a thickness that slots in snugly.

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Regarding the idea of setting the true angles with bolt - by definition this means you are incorporating elasticity in relative stiff system. Means also you have nice oscillation.

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How is it incorporating elasticity? Once the angles are set the bolts on the respective parts are torqued down clamping everything rigidly in place... you aren't relying on the part just resting on an eccentric bushing. Where does the elasticity come from?

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You are right system is relatively rigid. I am escalating problems caused G&T and consequences of those.

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You've lost me again lol - what's G&T when it's not in a glass with some ice?

I dont see a problem, as far as your face and back plate are actually machined on a mill.


Not that we are getting picky, but when some one sees that machine design, its obviously to a higher standard. So in order to maintain that standard and result to be incredible machine, one should aim high.

I said once somewhere, you may laugh but the most imprecision in a build comes from not wiping the dust correctly from rails when mounting, when you are alone and tired, in a rush and no one to help you.

Quote:

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Originally Posted by Zeeflyboy

Ok great, thanks - glad you agree with my thinking then!

I've just done a mass analysis on the finished machine and its coming in at just shy of 190kg... I know mass is but one suggestion of rigidity but that's not far off 3 times the mass of my current machine.

I've also taken the opportunity to change to a HGR25 rail and HGR25HA carriages on the Y-axis since there is more space now.

Had a quote back for all motion parts, it was pretty reasonable for ground screws and HIWIN rails. Think I'm good to pull the trigger on those parts?


http://i.imgur.com/kJvfLRJ.png

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This is certainly going to be one of the most beautiful and best machines I have seen. Seeing and following your posts I am sure that the quality will match the beauty and it will not just be a "beautiful blond" with only good looks and sexy appearance, but it will also have massive quality and accuracy attributes.

I also like the idea of protective side covers, I think this is important because of several reasons, apart from the most obvious that it keeps most of the chips inside the working table area, it also works pretty efficiently when the cutter is broken and comes flying at you like a deadly projectile at high speed. I also have side walls around mine and that have stopped two such projectiles already from hitting me, so it is definitely a good idea to design that protection from the start. I actually don't understand how other people dare to run these machines without any protection at all, some not even using protective goggles. Perhaps they never make mistakes and never break a mill bit, I don't know, but that's their business.

The only thing I'd do differently in your design regarding the walls is that I'd make them easily removable, preferably without the need of unscrewing. This is because it helps placing the work piece/vice/measuring instruments and so on on the table more easily. It also allows working on longer than the table work pieces if you would need it some day.

The other thing you should consider is the mass. 190kg is a very heavy thing, which is very good for a machine, but it sets some requirements for the table also. No point building such heavy machine if the table it is on is not stable enough, which I am sure you know very well also.

The other thing about the mass you have to consider is the ability to move it around. Perhaps it is a non-issue, but anyway, if you one day have to move it just a little bit, it is going to be a very difficult task if you haven't thought about that during the design. My machine is only about 90kg but to move that around on my own is not possible, so I have to lower the machine on wheels to do that, and even so it is not something which is done in a minute or two, first I have to lift the machine then remove the wooden blocks it is standing on then lower down on two wheels and do the same for the back, or the front part, depending on where I start. Mine is standing on it's own feet, so it is a bit easier than it would be for yours.

Perhaps you have these questions covered/solved already, but before starting the machine build, I'd build the table to build it on and made sure the table is extremely easy to rotate and move around during the work. It is going to be necessary to have easy access to all sides, that's for sure.

Anyway, it is very interesting to follow up on your work and see the progress. Good luck with the rest of the work as well, and don't forget too keep us updated, both here and on the Zone.

Boyan, you are clearly a man of high standards which I respect, and I thank you for your advice. I just hope that when I start building it doesn't become painful for you to watch ;)

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Originally Posted by A_Camera

The only thing I'd do differently in your design regarding the walls is that I'd make them easily removable

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It would be nice to have them removable, but they need to be water tight for underwater cutting of carbon fibre. I think making them rapidly removable may be tricky whilst also being sure I'm not going to flood my work bench. I get on okay with the current version which is quite similar, but I will have a think about whether I can do anything to make at least one side removable.

Quote:

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The other thing you should consider is the mass. 190kg is a very heavy thing, which is very good for a machine, but it sets some requirements for the table also.

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The table is crazy strong and rigid... In fact I think the table is probably 100kg or more itself! It's constructed from some very beefy pine struts, big slabs of 18mm moisture resistant MDF and topped with 40mm solid oak.... here are some pics from when I was building it with one of my friends just out of interest (not that you asked):

Main frame:

http://i.imgur.com/ZEpjPq0.jpg


Skinned and being massaged to perfection

http://i.imgur.com/lpAFJNa.jpg

http://i.imgur.com/evRYuHb.jpg

Controller mount and utility draw:

http://i.imgur.com/EgQ1WXS.jpg


Finished table:

http://i.imgur.com/OUuTaHR.jpg

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The other thing about the mass you have to consider is the ability to move it around. Perhaps it is a non-issue, but anyway, if you one day have to move it just a little bit, it is going to be a very difficult task if you haven't thought about that during the design. My machine is only about 90kg but to move that around on my own is not possible, so I have to lower the machine on wheels to do that, and even so it is not something which is done in a minute or two, first I have to lift the machine then remove the wooden blocks it is standing on then lower down on two wheels and do the same for the back, or the front part, depending on where I start. Mine is standing on it's own feet, so it is a bit easier than it would be for yours.

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It won't need to move very often, but when it does it will probably be a case of having to separate the gantry and the main bed... unless I just pick up an old engine hoist perhaps. Actually that's not a bad idea - perhaps I should built in some hoist points?

Moving heavy things is ultimately just an engineering challenge!


Just in case any one is interested, this is the Man Cave I built last year, which is the home for this future machine.... I also have to try and find space for a Wabceo D4000 lathe:

http://i.imgur.com/fYzY7vn.jpg

http://imgur.com/ljXUsNi.jpg

http://imgur.com/RpIafBr.jpg

http://imgur.com/yxOTHI2.jpg

http://imgur.com/esb13RU.jpg

Very nice place, but of course, I am not surprised to see that you man cave looks this nice and tidy. Thanks for sharing the images.

Otherwise I agree, moving heavy objects is just an engineering question but it is good to consider it in advance.

Thanks

Yeah you might have saved me some grief by making me think about hoist points early on!

Slight tangent again but I just wanted to share this beautiful bit of kit that just landed on my doorstep...

I've been quite excited waiting for this to arrive:

http://i.imgur.com/IbWO1jJ.jpg


It's a 3D touch probe called the TPA2 by Kurokesu... absolute piece of art! It's filled with di-electric oil (de-oxit I'm guessing) to prevent oxidation of the Tungsten carbide contacts which should keep it working reliably for a long time!

Looking forward to getting this up and running, if it works half as good as it looks it should bring a new level of accuracy to my work. I was waiting for this before kicking off any machining for "El Beast" so that I can use it to verify dimensions and for accurate two sided machining.


edit - got the concentricity at the tip dialled in to a consistent +/- 0.002mm so 0.004mm total.... just pushing hard on the spindle causes more variation than that on this machine so I think that is good enough for now!

http://i.imgur.com/ARJxbN0.jpg


https://www.youtube.com/watch?v=LAFG...m-upload_owner

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Originally Posted by Zeeflyboy

Thanks

Yeah you might have saved me some grief by making me think about hoist points early on!

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Sorry. :courage:

Wheels are in motion... Rails/carriages/screws/accessories have been quoted and paid for, and I've managed to get the milled bottom frame extrusions ordered too. I am having some 1204 screws ground for a different project which will unfortunately mean around 20 days lead time on the motion components, but this isn't going to be a quick build anyway as I'm going to be held back by only budgeting a small amount each month towards it's completion.

Looking forward to be able to get started on some of it. Plan is to build the bottom frame first as I have enough 20mm eco-cast in stock to get cracking and the extrusions should arrive middle of the month. It'll also be good to get that built first to make sure I don't have any alignment issues with the design, if I end up having to change how it's oriented then better to get that nailed first then figure out the changes that the X-gantry would require as a result.

Looking forward to the build....:thumsup:

So I've just got my hands on the extrusions...

http://i.imgur.com/OwsNDDc.jpg

http://i.imgur.com/eYuFwaT.jpg

Packaging looked okay but alas they weren't quite as well protected as one might hope - upon inspection one of the large extrusions has clearly suffered a drop on one corner.

http://i.imgur.com/NxeyzrM.jpg


Cleaned up with a file and it shouldn't have any impact on the final result.

http://i.imgur.com/X3YZnSz.jpg


To do a quick and easy check of comparative length I placed the extrusions on a piece of alucast plate and put them side by side. Given that a fingertip can detect features in the 10 micron range through dynamic touch (i.e. dragging your finger across a feature) this is actually a surprisingly accurate method of determining if there is any difference in length.

http://i.imgur.com/3mg5HiY.jpg

http://i.imgur.com/urfH2ru.jpg


The good news is that they seem to be completely flush and more-over standing them side by side you can't even see a hint of daylight between the two, so they must be nice and straight as well.

Did the same for the smaller cross-extrusions where it's arguably much more important that they are of consistent length and the initial check seems good too. As these are shorter than the main extrusions they should be within my ability to measure using the CNC machine and a touch probe, so should be able to get some more scientific results!

http://i.imgur.com/q5xyODf.jpg


Interesting to see the difference between the milled sides and the un-molested sides - you can see the gaps between the non-milled edges where they aren't flush (the edge that runs horizontal left-right in the pic)

http://i.imgur.com/hF0PxCK.jpg


Quick layout to see the size:

http://i.imgur.com/1Y6cLpW.jpg


Next month's budget will go on some alu plate and some thorlabs precision corner brackets (well, and a big bbq for a new built in project I'm doing in the garden!) , and then the build of the y-axis can properly begin, hopefully with the motion components arriving some time next month too. Apart from the unfortunate corner ding, I'm very impressed with the quality. They are some seriously chunky and solid feeling hunks of alu too which is reassuring.

Nice, thank you. Care to share the supplier and the data? Maybe next time I'll buy these, since these look MUCH better than mine.

About the dent... you should complain. I received once also one with a dent, complained and without further discussion they sent me a new piece. Yes, it is just aesthetics, but it is a pity to have spend so much time and money on perfection and on something which (especially in your case) is otherwise so nicely designed and built and start off with a dent... :chargrined:

I thought about that, and I may yet do so... The problem I'm thinking is that it really helps me out if these are perfectly matched length wise. Given that I'm sure they set the cutting length and then chopped one after the other, when done as a pair they should be pretty much spot on. If they send me a single one to replace the dinged piece then there is no guarantee that it will be as closely matched and will be subject to their cutting tolerance instead (which they don't actually seem to specify, other than allowing you to dictate product length in 0.5mm increments).

So given that consideration, along with the fact that the corner will be totally hidden once constructed, I'm leaning towards just sticking with it rather than risk extra alignment headaches by slightly mismatched lengths.

But anyway, to answer your question the profiles themselves are pre-milled pieces from misumi. The cross pieces are HFSP8-5050 (50mm square profile, milled on 2 sides - so actually 49x50mm) while the larger ones are the bulkier high rigidity GFSP8-10050 (100mm x 50mm, milled on the 100mm sides, so true dimensions are 100x49mm). Misumi have a variety of milled profiles so you can probably find one that suits what you need - the issue is actually ordering it if you don't work for/own an appropriate company as they won't sell to normal plebs like us.

Looks very nice. I've heard good things about Misumi extrusions and they were one of the sources I had considered using in the past but I've never ordered anything from them. Thanks for the pics. They confirm my perception of Misumi's quality. Given the quality of the extrusion, do you think you really need the Thor Labs corner brackets? Looking forward to your build...

There is probably an argument to be made that I could live without them...

Maybe I'll go with just a single pair at the front and see how it comes out... easy enough to add a second pair at the back if required.


On a related tangent I've been working on a custom tool drawer insert for my CNC bench... still haven't placed all tools yet as I haven't fully decided what I want to put in... also need to make the handle in the front.


http://i.imgur.com/9yTQaYT.jpg

http://i.imgur.com/64vAP8O.jpg

http://i.imgur.com/2wrVWJA.jpg


https://www.youtube.com/watch?v=EmsdlI6nCVQ

So as promised, something more scientific....

I used my touch probe to measure the length of the cross braces. Fairly impressive cutting tolerance really I suppose, the nominal length was 344mm and the longest was 344.34mm while the shortest was 344.28mm so they are within 0.06mm of each other. Would have been even more impressed if they were all 0.3mm shorter :playful:

http://i.imgur.com/iEia1AN.jpg

http://i.imgur.com/rnzPGoB.jpg

http://i.imgur.com/1MUxB8U.jpg


So my options are to use some shim material to make them all up to an effective 344.34mm or I can try to nip them all down to 344mm on the CNC... Shimming is probably the least risk route.

Got home today to find FedEx had left me a nice treat:

http://i.imgur.com/xyLmFI0.jpg


My linear motion stuff arrived, and initial inspections it all arrived intact. HG25 rails and carriages could probably be used for seal clubbing if one were so inclined... didn't realise quite how beasty those are.

Quality of the TBI ballscrews looks to be fantastic - finish is excellent, as is the end machining and they are as straight as an arrow with absolutely no discernible slop or play on the ballnut. I intend to do some tests with the glass scales just to see what that tells me but from a visual inspection stand point they seem top-dolla!

some linear motion porn (NSFW?)


http://i.imgur.com/Wtpg5po.jpg

http://i.imgur.com/MLR2J4A.jpg

http://i.imgur.com/8BJ9979.jpg

http://i.imgur.com/s74dYYQ.jpg

http://i.imgur.com/PAsXLcU.jpg


Had a bit of an order snafu with Thorlabs - got an order receipt and they reserved funds on my bank account but the order didn't get processed. I have spoken to them and re-ordered so those should be arriving shortly. Other than that I'm just waiting on an order from motedis for various extrusion related fixings and then I should have most of what I need for the bottom frame build.

Out of curiosity, where did the linear motion bits come from?

Topper on aliexpress... I was dealing with a guy that goes by the name of John (I would assume a western friendly name!) - very helpful chap. Just emailed him asking for a quote for all parts with details of what I needed and then they can create a special order for you on aliexpress so you still get the buyer protection afforded by them.

I was one HD16 short (can't really complain since they threw those in for free) and I've sent an email to enquire about that so we'll see what they say. They do both TBI, HIWIN and they do their own factory Chinese made stuff too which would work out quite a bit cheaper. For this machine I went with the HIWIN rails and C3 TBI screws, for my other project I went with some of their own factory manufactured ground screws and nuts which were significantly less than the TBI equivalent (C5 ground 1204 screws are very expensive it seems!). On first impressions those factory own screws look well made too, and while they don't have any discernible play on the nut they aren't quite as smooth to spin by hand as the 16mm TBI ones for El Beast.

Was very happy to see the end machining has been done to a very high standard - bearings are a snug fit and the machining is concentric. All the other parts like rails, carriages, MBA-12C mounts, FK and FF bearing sets seem high quality - So far so good.

As mentioned I want to check the screws against the glass scales just to check lead error and consistency more out of interest than anything else, but having had a good look at them I would be surprised if they were anything other than excellent.

Did a little machining today... found some nice little extrusion connectors at motedis which will work nicely at pulling the two side extrusions together:

http://i.imgur.com/i1mWQS9.jpg


There is a rather pricey drill bit and jig that you can buy to put the hole in the extrusion at the right spot, but I figured it was just as easy and much cheaper to use the CNC instead. I just 3D printed some little work alignment jigs so that I didn't have to re-zero between each setup:

setting up:

http://i.imgur.com/53xS3dV.jpg


Milling using a fairly long 8mm bit to a depth of 36mm

http://i.imgur.com/X6Xwd9m.jpg

http://i.imgur.com/MFIeInr.jpg


Fits nicely:

http://i.imgur.com/Agk8lcS.jpg

http://i.imgur.com/Htp75AJ.jpg


Oh and Thorlabs brackets arrived last week - I've just gone for the front ones at the moment given that they are certainly not cheap. Will wait to see whether I think the rear ones are a good idea or not.

http://i.imgur.com/kNE73g5.jpg

Looks like it will be an extremely high quality machine!

I have a question which you will probably find quite noobish but I am interested in your glass scales. Specifically, how do you use the glass scales in a feedback loop to control your position? Does the position from the scales get fed back into the motor driver and that corrects any error? Or is the position fed back into your break out board and on to your motion controller?
The reason I ask is if you have position feedback​ from a linear scale any backlash in your drive system wouldn't matter?? Then theoretically one could use c3 screws instead of c7 for instance. Or, standard gearboxes instead of low backlash units. Am I thinking correctly here??

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Quote:

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Originally Posted by 1Jumper10

Looks like it will be an extremely high quality machine!

I have a question which you will probably find quite noobish but I am interested in your glass scales. Specifically, how do you use the glass scales in a feedback loop to control your position? Does the position from the scales get fed back into the motor driver and that corrects any error? Or is the position fed back into your break out board and on to your motion controller?
The reason I ask is if you have position feedback​ from a linear scale any backlash in your drive system wouldn't matter?? Then theoretically one could use c3 screws instead of c7 for instance. Or, standard gearboxes instead of low backlash units. Am I thinking correctly here??

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I simply use the glass scales for calibration purposes. They were mainly the answer to my current machine's less-than-optimal screws - I simply adjusted the steps per unit to match the scales. In mach3 you can actually go deeper than that and map the ballscrew to compensate for variation along the screw itself too, but I never went that far.

Certainly it is possible to link a positional encoder such as a glass scale and a CNC controller to give absolute position feedback, but I haven't looked into it too far as for my needs the calibration was sufficient. I think linuxCNC has a way of using it.

It certainly would be a good way of compensating for lead inaccuracies and variation - I don't think it would do a great job of controlling excessive backlash though, but then most semi-decent ball screws don't have much backlash anyway. If you had a lot of backlash it would have to be very quick to arrest movement to stop chatter and poor edge surface finish, there is never really a good solution for backlash other than to remove it.

BTW I think you have the C's backwards, the lower the C number the more demanding the specification... so in your example it would more be a case of it allowing you to use c7 rather than more expensive c5/c3/c0. Of course good glass scales aren't cheap either so it's debatable as to how much saving you would make.

Edit - EMC2 can do it too apparently.

Edit 2 - also came across this quote which pretty much describes what I was thinking regarding it not being a cure for backlash:

Quote:

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But, a caution: Knowing position via the glass scales doesn't
eliminate the backlash problem. The real problem is that the
position of the table is not constrained in both directions by
the servo. it is only constrained in one direction at a time,
and the motor cannot hop from one side of the backlash to the
other instantly, therefore cutting forces and inertia can flip
it from one side to the other faster than the motor can
compensate. This can lead to messed-up parts, broken tools and
general foul language around the shop. So, don't think the
glass scales are some kind of panacea that allows you to do
precision work with sloppy leadscrews.

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Got it. Thanks!

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