-
1 Attachment(s)
Let The Fun Begain, New build on the Table.
Hi All,
My name is Mike and I am about to start building my very first CNC router,
I will need a lot of help with this and I hope I can count on you all to help. I will change some of my design to what you tell me but I might reject some and go with my own ideas.
Anyway My main Hobby is building and flying Radio Control Scale models and I hope to make some model kits of planes that I have designed along with Retracts etc to help recoup some of the money that I will be putting into this machine.
Now with this in mind the main thing that I will be cutting is Ply, balsa, and aluminium for the most, But of course I will have to try house signs wooden toy and any thing else.
The rails will be Supported linear rails SBR20-300mm SBR20-650mm SBR20-1100mm with the Bearing Blocks.
And the ballscrews RM1605 - 350mm - 700mm and I will use twin ballscrews - 1150mm This I cannot change as I have them waiting for me on my bench.
Now I purchased some 6082 aluminium for the Z axis which is 20mm thick 330mm x 160mm and I was surprised at the weight 3.4kg.
The first question of many.I was planning to use these steppermotors, Will the Nema23 Stepper Motor 3.1Nm be strong enough to work this ( the weight of aluminium four bearing and a router. ) I was going to use these straight without gearing? I have attached a drawing of the Z axis ( I hope ) to let you see what I'm thinking about.
-
Re: Let The Fun Begain, New build on the Table.
I advise you read some of the build logs on this forum, as it is evident from the Z-axis design, some of the parts you have chosen and the question you ask, that you would do well to find out more before building this. For example, it's stronger to put the Z-axis rails on the same plate as the spindle and it would have been better to have RM1610 screws for X and Y.
20*330*160*2.7*10^-6=2.85kg, so either your scales are wrong or the dimensions of that plate are greater than specified.
3.1Nm motors will be plenty. Using timing belts and pulleys has numerous advantages, including getting better performance by changing the drive ratio, making it easier to mount the motor and helping with resonance damping. Since it seems you have bought 5mm pitch screws for X and Y, you will almost certainly need to use a 2:1 ratio (bigger pulley on motor) to make the machine run fast enough. Again, this information is nothing new - read a few build logs and you'll be able to answer the questions yourself.
-
1 Attachment(s)
Re: Let The Fun Begain, New build on the Table.
Ok my mistake it is 2.85Kg and not 3.4Kg I made the mistake when I converted from 6.283Lbs to Kg.
Right now we know I'm an idiot I have changed the design round to the rails on the same plate as the spindle, The reason I did it the other way round was there would be less weight for the stepper motor to lift, I also have a question about the gearing, If I used a 2:1 will I not lose torque but gain the speed from the stepper motor?
Here is my new drawing see what you think, I would have liked to put the two bearing blocks in line with the gantry blocks but i would lose a lot of travel, Anyway how high should I make the bottom of the Z mounting that holds the router from the table. Attachment 8737
-
Re: Let The Fun Begain, New build on the Table.
Hi,
As Jonathan said this is all covered in most of the previous builds. Revised plan is much better but you could gain a bit more rigidity by moving the lower block down to match the end of the rail as your z axis blocks look a little close. The z axis is the weakest part as it is a cantilever and will flex the most, A larger distance between the blocks will also reduce the bending moment on the y axis (rotational lever arm effect) What travel where you looking for?
The z axis blocks don't have to be in line with the gantry blocks and it might be worth centralising them on the plate so the bottom of the router plate is in line with the bottom y axis beam as that will mean you can lower the gantry sides (whilst retaining the same clearance)to reduce the force on the x axis bearings.
My comments are only to help maximise the performance of the parts you have and are not a critisim of your design. Happy building
Edit. whilst supported rail is stronger with regard to the rail, the bearing is weakened by not completely wrapping around the bar therefore the bearings have reduced strength when pulled away from the rail , this is easily solved by mounting the rails back to back, or in your application on top and bottom rather than on the side. For example in your sketch when the gantry moves to the left the z axis (due to cutting force) will rotate about he lower bearing on the y axis and try to push the top bearing (strongest direction) how ever when the gantry moves right it will still rotate about the lower bearing but now will be pulling on the bearing which is the weakest direction.
Again this point is just a way of maximising the machine strength by design and I'm not saying that the method you have proposed is not good enough as it is probably more then adequate for most uses but my option just increases strength for free....
Height of the gantry needs to be as lower as possible but allow for the max depth of you work + how deep you need to to cut. for example if you work piece is 50mm and you want to cut all the way through you need to allow at least another 50mm for the cutter + shank and collet so say 125mm.
-
1 Attachment(s)
Re: Let The Fun Begain, New build on the Table.
Hi Ross77
Right here I am again with the Mk10 drawing of the Z axis, I may see one or two other ways of doing this but I thought I would let you see where I am at this point.
I have about roughly 120mm of travel in the Z axis.
Now about the height from the bottom of the router mounting to the table top. Do you mean that would be 125mm?
Attachment 8755
-
Re: Let The Fun Begain, New build on the Table.
Yep that looks good. Mk10? so you have only just started then:friendly_wink:
I would increase the distance between the y axis rails to match the z axis plate to increase bending and torsional resistance.
If you have mounting clashes with the blocks then widen the plate, it would be best to make any compromises on the y axis side of things as this is more forgiving than the Z axis.
Yes I did mean 125mm from the bed to the router base. Is that not what you were asking?
-
Re: Let The Fun Begain, New build on the Table.
Thanks Ross77 yes that is what I needed to know, I was just double checking Before making any more adjustment. I appreciate your help.
-
Re: Let The Fun Begain, New build on the Table.
Just thought I'd better check but the 125mm was only an example, actual value will depend of your router collet and cutter length.
What router/spindle are you using? can it be fixed at the top as well? as the L shaped mount is also a bit weak.
-
1 Attachment(s)
Re: Let The Fun Begain, New build on the Table.
I have now reinforced the L shaped mount. Its now braced right to the top now.
The router that I will be using is the Kress 530 with a 3.175mm and a 6.35mm collets and I was going to get the mount from CNC4YOU.
Here is the latest drawing of the Z axis.
Attachment 8782
-
7 Attachment(s)
Re: Let The Fun Begain, New build on the Table.
-
Re: Let The Fun Begain, New build on the Table.
Quote:
Originally Posted by
Bush Flyer
Here are the final drawings
No they are not at all final, they're still crap :very_drunk:
Look at the distance from the tool tip to the bearings above. 3 miles is too much.
Find a good solid cardboard box. Remove front and back. Try standing something on top.
When you figure out how to stop it collapsing, go back to your router drawing and try again.
-
Re: Let The Fun Begain, New build on the Table.
Quote:
No they are not at all final, they're still crap
Harsh but fair eh Robin.
I would agree that the gantry sides are way to slender. You either need to reduce the height of the y axis or thicken up the side plates with some of that profile section. Having now seen the whole design I would reiterate my earlier comment about increasing the distance between the y axiz rails as that will reduce the torsional force on the gantry sides and also give a better ratio of supported to unsupported plate (not sure if that's the best way to describe it?)
The Z axis is way to complicated , get rid of all the blocks and wedging plates. i.e. make the bottom plate as one piece that bolts to the bearing and is also the spindle mount. Do the same with the top plate and make it bolt to the bearing and be the ball screw mount. this will make it lighter, stronger and much easier to build.:smug:
Keep at it, as its worth getting right before you start building.
-
Re: Let The Fun Begain, New build on the Table.
OK I give up and have deleted all drawings to start again, But before I start with a new drawing please can you send a quick sketch of your cnc or a picture as I did not under stand what you mean about the bottom plate as one piece that bolts to the bearing and is also the spindle mount, Remember I have no machining ability so I will be buying the aluminium cut from the supplier at 20mm thick and cut to size as I am disabled and could not hacksaw 20mm thick aluminium plate. But I do have a drill press. I Have been copying some designs but have been adding some extra bracing etc. So now I have a blank screen on my computer and before I start again it would be nice to see your CNC or where to find your build to give me some help in the design.
-
Re: Let The Fun Begain, New build on the Table.
Quote:
Originally Posted by
Bush Flyer
OK I give up and have deleted all drawings to start again
Oops, lets not over-react, don't empty that recycle bin quite yet. But you are making a newbie mistake :frog:
There is no set way of doing this, best way depends on what you have to work with and what you are trying to achieve.
The newbie mistake is guessing that at some nebulous time in the future you will want the gantry to clear 6".
In the real world you do 99% of your cutting in the bottom 1" because that is the length of your average router bit.
Get it wrong and 99% of your cutting is done at full tool extension and the machine tries to shake itself to bits.
Q1: What height does your gantry need to clear?
-
Re: Let The Fun Begain, New build on the Table.
Having designed and working with a machine with the C style gantry I would strongly suggest IF possible to move the C so that the Screw is behind it to protect the screw from swarf (I have to clean mine often). While you really do need to increase the rigidity of the gantry supports, that can be done a couple of different methods.
1) go to extrusion for the gantry sides (the solution used on my machine)
2) Increase thickness and add full running ribs to add even more rigidity
3) Increase thickness even more then above and add partial supports to help transfer force to the plate you use for the x axis rails
I would not only go through the build logs here but also go to places like , shopbot, CAMaster, MultiCAM, and a few others and look at those machines and their designs. One of the items about hobby CNC machines is they are often over built. It is not a bad thing but it can add to the expenses without reason. The use needs to be taken into account in the design. Building a machine that can cut steel for doing MDF is over kill and funds used poorly.
Good luck with the design and keep posting, don't mind the gruff from any of the folks here, it is normal and you just take on the information and let the rest go.
Michael
-
Re: Let The Fun Begain, New build on the Table.
Quote:
Originally Posted by
m.marino
Having designed and working with a machine with the C style gantry I would strongly suggest IF possible to move the C so that the Screw is behind it to protect the screw from swarf
That can be done, however you need to be careful not to have the ballscrew far from the Y-rails and spindle, otherwise the stiffness of the axis will be greatly reduced.
-
3 Attachment(s)
Re: Let The Fun Begain, New build on the Table.
Apologies if my comments seem harsh, I am only trying to help you make your machine as strong as possible and easier to build.
My Machine is still on the drawing board and is way different from yours anyway. if I get time I will sketch some thing out for you.
I've attached a design I started 4 years ago but abandoned as I needed a stronger machine, you might be able to adapt afew bits. The z axis has the one piece top and bottom plate I was talking about and also the raised x axis rails might suit your design as it makes the gantry shorter and still gives a good depth of cut. Its not a finished design so I know its not perfect.
Quote:
That can be done, however you need to be careful not to have the ballscrew far from the Y-rails and spindle, otherwise the stiffness of the axis will be greatly reduced.
That was my thought as well, you would place the ball screw under unnecessary load by having the link bar go around the beam to the z axis. better to cover the ball screw with bellows. Or if you make the c section deeper to increase the y axis rails then the ball screw could be moved to the top so out of the way of chips.
Happy building
-
4 Attachment(s)
Re: Let The Fun Begain, New build on the Table.
Hi all,
Here is my new drawings for my 1100mm X 700mm X 300mm CNC, the only thing that I kept was the bed, everything is new from there.
I lowered the height of the gantry the Z axis from 125mm to 55mm (that's back to the height that I had my very first drawing) from the bed that should let me put a thin mdf board as a sacrificial board. The travel in the Z axis is 110mm.
The gantry sides are made out of two 20mm thick plate aluminium which will be bonded and bolted together, the first one is solid the second one will be lightened. The Z axis will also use 20mm plate aluminium. The backing on the Y axis is 12mm plate aluminium bolted to Aluminium Profile Extrusion. And the X axis can easily be stiffened buy adding more Extrusion to the Bed if needed.
Ross77,
Thanks for letting me see your drawings, and I have seen this design before and dismissed it as being to difficult to build. The welding part is easy but to make it accurate would mean a lot of shimming, as you know welding one side of the metal joint twists the steel one way and when you weld the other side of the joint it will pull it back again. I am not longer able to Cut and grinding steel due to now being disabled. But I do like the Z axis and I would like to see a photo of your machine.
Attachment 8846
-
Re: Let The Fun Begain, New build on the Table.
A quick thought!
Flip the 'Y' axis (top to bottom) arrangement over and add another plate to the back to mount the ballnut and you will always have a nice clean screw :thumsup:
-
Re: Let The Fun Begain, New build on the Table.
Looks good mate. are you happier with this as well?
Whilst myself and others could carry on making suggestions to tweek if further I think you have got to the point of a build-able machine, without going into calcs you have gone as far as you can.
The only point I would make and it is minor and that is that you might need to add additional support to the top of the X axis bearings to stop them opening up due to the weight of gantry, placing the rails and bearings on their side will improve load capacity but some of the cheaper bearing holders can give and open up the bearing.
I apologise for misleading you with the table distance as I presumed you meant with the z axis at the top of its travel. I see from your drawing you are talking about it a full extension.
Quote:
I have seen this design before and dismissed it as being to difficult to build
yep thats one of the reasons I abandoned it, cheap but difficult to build. I was mainly showing it to you for the rail orientation.
Quote:
The welding part is easy but to make it accurate would mean a lot of shimming, as you know welding one side of the metal joint twists the steel one way and when you weld the other side of the joint it will pull it back again
The design was actually for Ali sections and they would have been bonded with epoxy and riveted for good measure. that way no distortion due to welding.
I never got around to building it so no photos I'm afraid.
-
Re: Let The Fun Begain, New build on the Table.
Quote:
Flip the 'Y' axis (top to bottom) arrangement over and add another plate to the back to mount the ballnut and you will always have a nice clean screw
where's the fun in clean? yes you can do that but moves the ball screw away from the Z carriage and reduces rigidity and can lead to racking or binding of the bearings the extra distance can mean the alignment would be a mare as well.
Edit. thought id seen that mentioned before! just realised it was this thread, so same as Jonathan's answer
-
Re: Let The Fun Begain, New build on the Table.
Quote:
Edit. thought id seen that mentioned before! just realised it was this thread, so same as Jonathan's answer
There you go great minds think alike. The distance is minimal and would not make any noticeable difference. As for binding then you need to make allowances in the bolt holes so that you have adjustment
-
Re: Let The Fun Begain, New build on the Table.
Hi Paul
yeah I agree that it probably wont affect the performance to much but without going through all the calcs and then changing/ widening bearing spacing to compensate then it is best left as it is. remember this is being built with a pillar drill so ease of fabrication and also dimensional tolerance is less than parts made on a mil or cnc.
the binding is as a result of the lever arm of the system. the original set up was Bearing-Ballscrew-Load so the ballscrew can control the load directly. moving the ball screw back results in Ballscrew-Bearing-Load so the ball screw has to work through the bearing to contol the load and vice versa, the load is transmitted through the bearings before the ballscrew can control it. Under sudden loads this can cause the system to rotate around the bearing and as open linear bearings have clearance they could bind or cause premature wear.
Again it can be designed out but I think it will be easier to just clean the ball screw
-
Re: Let The Fun Begain, New build on the Table.
Sorry Ross in this instance i would have to disagree. Swapping it over as i said would result in the ballnut being roughly in the same position, as the plate showing on the 'Z' could be set further back still. For this type of build it will work absolutely fine. Have a look around the forum with such a design and ask how they are getting on ;-)
-
Re: Let The Fun Begain, New build on the Table.
Its good to know that I'm heading in the right direction, and I am happy with the progress so far.
-
Re: Let The Fun Begain, New build on the Table.
Moving the ballscrew, whilst not disastrous, hardly gains anything. All you're gaining is some protection for the ballscrew from swarf and there are plenty of other ways to do that - for example adding seals or bellows. So even if the difference to the overall machine due to the loss in rigidity is small, you're doing this to correct a problem which is also very small since it's clear that swarf on the ballscrew is also only a small problem. I recall Jazz saying he'd worn out his ballscrews from letting the swarf pile up on them over a few years, but I've not come across anyone else who has had a ballscrew (or nut) fail for that reason.
Quote:
Originally Posted by
Swarfing
For this type of build it will work absolutely fine. Have a look around the forum with such a design and ask how they are getting on ;-)
Having the ballscrew on the back on my machine has crippled the stiffness of my Y-axis and although the distance is greater, that shows how the effect can be significant.
-
Re: Let The Fun Begain, New build on the Table.
When I am finished with a tools I am probably OCD about keeping tools clean and put back ready for the next time, It's the same when building a new RC model before finishing for the day I will tidy up and put all tools back where they come ready for the next time, and I have always been like that so keeping the ball screw clean will not be a problem.
-
Re: Let The Fun Begain, New build on the Table.
Quote:
Having the ballscrew on the back on my machine has crippled the stiffness of my Y-axis and although the distance is greater, that shows how the effect can be significant.
Correct Jonathan yours was a huge distance from centre hence your issue. Switching would save a lot of hassle having to sort extras like seals and way covers etc. My suggestion was a sound one but the choice is yours of course. BF your design is a good one i would like to point out and will work great without the changes so well done. Building these things is a costly venture and you spent the time listening and looking at what works already. Mine is no way near as good as what you have so you should be in a good place.
-
Re: Let The Fun Begain, New build on the Table.
Quote:
Quote:
Sorry Ross in this instance i would have to disagree
No need to apologise, the more opinions Mike gets the better.
Quote:
Quote:
Swapping it over as i said would result in the ballnut being roughly in the same position,
Yes but it would need a link arm or bar to connect back to the bearings hence lever arm. It just seems odd to me that people use ball screws to rid of backlash to 0.01mm and then mount them in systems that deflect more than that.
I still agree with Jonathan and don't see why you would risk compromising machine ridigity just to keep a ball screw clean, that's what guards are for :chuncky:
Any way i think this point has been laboured enough and mikes happy to keep his tool clean......
-
Re: Let The Fun Begain, New build on the Table.
Quote:
Yes but it would need a link arm or bar to connect back to the bearings hence lever arm.
Mmmm! not sure what you mean here? If you are making a box to encompass the supporting rail then you are actually increasing rigidity. The bearings will be supported both sides of the fence so to speak so can not for the life of me see how it is worse? the ballnut will still be roughly in centre and mounted on the backplate. I really don't see what there is not to understand here.
-
1 Attachment(s)
Re: Let The Fun Begain, New build on the Table.
Quote:
Mmmm! not sure what you mean here?
Ok better explain myself in case I'm wrong. :nevreness:
Just to make it clear thought that its only because open bearings and supported rail are being used with a small bearing centre to spindle nose distance ratio. Ideally the bearing centres (on plan) should be increased but given Mike has already redesigned it a few times I didn't want to offer any more changes without justifying them with calcs.
Quote:
If you are making a box to encompass the supporting rail then you are actually increasing rigidity.
Yes but its not so much the bearing mounting but the bearings themselves, open bearings can have quite a large radial clearance (10 to 50 micron), with the current set up and using a conservative 10 micron clearance (could be to 50), 100mm bearing spacing and 200mm spindle distance that results in 39 micron of free movement at the spindle. moving the ball screw the other side increases this to 51 micron.
This is free movement just to take up play, if you add any deflection due to load then this will obviously increase further. for cutting Ali the open bearings can run close to the max load capacity and as rigidity is a function of imposed load and load capacity then deflection will be high.
On the face of it 10 micron is a very small amount but remember this is only One element and doesn't include deflection in the part. if you lose 10 micron at every junction then it all adds up to a considerable amount.
Any way that's my take on it!
-
Re: Let The Fun Begain, New build on the Table.
Ross i did say that the plate could be moved further back. In this design there is no reason why the ballnut could be more central and the spindle moved closer to centre. There is no need to have the nut pushed further away from centre.
-
Re: Let The Fun Begain, New build on the Table.
Quote:
Originally Posted by
Ross77
Ok better explain myself in case I'm wrong. :nevreness:
I thought your first explanation was good, but the latest one is even clearer. I agree with the 39-51um figure and as you say it's likely to be more. Any compromise like this will reduce the stiffness of each element. You can analyse the stiffness of the overall machine as springs in parallel, so if you reduce one a very small amount it's not likely to make a tangible difference, however if one is reduced substantially such that the stiffness is lower than other elements, then that will dominate the system, causing the overall stiffness to be low. This means compromising one part can waste money you've spent on other quality (stiffer) parts. An extreme example would be using profile rails on two axes and unsupported rails on the other. In that instance changing the profile rails to supported rails isn't likely to make a difference, since the weak point would still be the unsupported rails. Similarly, 'making a box to encompass the support rails' wont make much difference, since that part of the assembly is already at least an order of magnitude stiffer than other parts.
You can get the ballnut in a more optimal position with the current design - it doesn't have to go behind to do that. Similarly the current design could easily have a 'box to encompass the supporting rail' added.
Quote:
Originally Posted by
Swarfing
Switching would save a lot of hassle having to sort extras like seals and way covers etc.
Just stick a 15mm shaft seals, like these, either side of the ballnut and the swarf is wiped off easily. They're working well for me and not showing signs of wear, although admittedly I've not been using them for long.
-
Re: Let The Fun Begain, New build on the Table.
Quote:
Ross i did say that the plate could be moved further back. In this design there is no reason why the ballnut could be more central and the spindle moved closer to centre. There is no need to have the nut pushed further away from centre.
Paul I think we must be looking at different drawings:friendly_wink:
If you look at the Z axis drawing in post #18 there is barely enough room to flip the plate over. if you then centralise the ball screw you will have to move the Z axis assembly further away, making the situation much worse.
As I said there are other more pressing issues with the design but as the parts are bought and he wants that size working envelope then there's not much that can be done other than maximise the other components. Another reason for not moving the ball screw is that despite the large plate on the back the y axis could still twist if Mike decides to cut larger pieces of Ali. with the ball screw in the front it is a simple case of widening the y beam to increase its torsional rigidity.
Anyway I think we will just have to agree to disagree on this one.:beer: We all have different ideas and its up to mike to decide as ultimately he knows what is needed from the machine.
-
3 Attachment(s)
Re: Let The Fun Begain, New build on the Table.
Right, I have made one small change to the Y axis to tie it all together. So no more changed till it is built. I ordered some 6082 aluminium plate and have started to construct the Z axis.
I can only do a little at a time before the pain is to severe and I have to stop, It will be a slow build but I will get there. Anyway one drawing of the change and two pictures to keep you going.
-
Re: Let The Fun Begain, New build on the Table.
looks like some good progress Mike. that back plate will help stiffen it all up.
glad all the comments didn't put you off. keep it up
-
6 Attachment(s)
Re: Let The Fun Begain, New build on the Table.
Ok here is another part done I had to cut 3mm off the aluminium plate, as they came to large. Now the only way I could cut the 3mm off was with a hand held router and a M6 end mill with the plate held in a wooden jig. That was hard going. Anyway with stops to rest I did start to assemble the bed.
Attachment 8975Attachment 8976Attachment 8977Attachment 8978Attachment 8979Attachment 8980
-
Looking really good. Any estimations on how much you think this project will cost?
Just wondering.... Where did you source the aluminium extrusion from? Thanks
-
Re: Let The Fun Begain, New build on the Table.
Bit late now but a chop saw would have been a good investment for you if you have problems using a hacksaw.
With the right blade you could have cut all the aluminium both plate & profile yourself which would have made things a bit easier, plus it would also be handy for cutting aluminium to size before machining it once the router is up & running.
-
Re: Let The Fun Begain, New build on the Table.
Quote:
Originally Posted by
robump
Looking really good. Any estimations on how much you think this project will cost?
Just wondering.... Where did you source the aluminium extrusion from? Thanks
To get it up and running I hope it will not be more than £1500. I tried to work out what It would cost then added 22%, I cost the bolts at about £40 but it has cost £59 in bolts so you need to add about 22% to what you think it will cost I have done this with everything that I have made and it's stood me well. It will always end up at the higher price.