Comments sought on new build: A CNC Router for RC Gliders and Planes

Quick vid showing the drilling with the guide in place, I've not showed setting up to drill a hole as I'm sure that's pretty self explanatory...saying that so is drilling the hole...oh well :whistle:

The pillar drill is a bit old and knackered and I think could do with a little TLC....

https://www.youtube.com/watch?v=HBGuVm6FQKs

Did a bit of shopping on Friday and it turned up today :eagerness: I bought a 1200mm Veritas straight edge, a couple of 6" engineers squares and 4 100mm G cramps.

Placing the straight edge against the rail there was a bow in the middle of the rail of about 3 thou so I loosened all the master x rail bolts and clamped (lightly) the straight edge to the rail in 6 places. I then tightened the bolts checking with a feeler that there was no gap between the reference side of the rail and the straight edge. Once this was done I placed the straight edge on the reference side of the rail and tried the feeler gauge again. It was the same all the way down with no gaps so I'm happy with that. I'm going to clamp (lightly) the straight edge to the rail again and then one by one take out the M5 socket cap heads and threadlock them in. This should give me my master reference X rail to set the second X axis rail from.

Attachment 14399

I wanted to see if there was/how much twist there is in the rails. Placing the straight edge across the two rails on top of the carriages I tried to get a feeler gauge underneath the edge and couldn't. Shone a light from the other side and couldn't see a thing so it looks like the epoxy has done it's job in finding the level. Again I'm happy with that!

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Waiting on my Tooling plate to come before I square the second X axis rail so I'm just making drawings so I know where I'm drilling holes, machining pockets for steppers ballscrew housings etc, what size belts and pulleys to get etc. etc.

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Originally Posted by njhussey

Surely the twist will be sorted when the rail is bolted tightly down, that's assuming that the epoxy is perfectly flat of course?

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Quite likely yes - but how much force will bending the bearing to 'flat' impose upon it? The answer is a lot, since the stiffness of these bearings is still very high in the rolling direction. It also depends on how stiff the gantry is and how wide it is - something has to bend. A fairly high force wont make much difference to how smoothly the bearings roll, since as I mentioned in the last post their co-efficient of friction is very low. It will still shorten the life of the bearings though.

It's different with round rail bearings - clearly they have zero stiffness in the rolling direction, so angular misalignment doesn't affect the force of the bearings (within reason).

If you look in the datasheet for the rails and bearings you'll find specifications for the maximum linear and angular misalignment. These are based on getting the rated lifetime out of the bearings, so if you exceed it by a little, the bearings just wont last as long. Though on a home machine it might still outlive you!

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Originally Posted by njhussey

I wanted to see if there was/how much twist there is in the rails. Placing the straight edge across the two rails on top of the carriages I tried to get a feeler gauge underneath the edge and couldn't. Shone a light from the other side and couldn't see a thing so it looks like the epoxy has done it's job in finding the level. Again I'm happy with that!

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That's a good indication that they're close, but since you've got the straight edge you might as well measure it carefully. The issue with what you just did is it's hard to measure very small angles and you don't get a reading for what the angle actually is. Instead you need to do something like in my build log - stick the dial indicator on one of the bearings and mount the straight edge parallel to the rail, but some distance (say 200mm) horizontally away from it. Make the indicator touch the straight edge, with it's movement perpendicular to the surface. That will convert the angular reading into a linear reading and amplify it. You don't need to worry too much about getting the straight edge level, as if you plot the readings on a graph that will just make a linear error which you can subtract.

Just out of interest, how much did the straight edge cost?

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Originally Posted by Jonathan

Quite likely yes - but how much force will bending the bearing to 'flat' impose upon it? The answer is a lot, since the stiffness of these bearings is still very high in the rolling direction. It also depends on how stiff the gantry is and how wide it is - something has to bend. A fairly high force wont make much difference to how smoothly the bearings roll, since as I mentioned in the last post their co-efficient of friction is very low. It will still shorten the life of the bearings though.

It's different with round rail bearings - clearly they have zero stiffness in the rolling direction, so angular misalignment doesn't affect the force of the bearings (within reason).

If you look in the datasheet for the rails and bearings you'll find specifications for the maximum linear and angular misalignment. These are based on getting the rated lifetime out of the bearings, so if you exceed it by a little, the bearings just wont last as long. Though on a home machine it might still outlive you!



That's a good indication that they're close, but since you've got the straight edge you might as well measure it carefully. The issue with what you just did is it's hard to measure very small angles and you don't get a reading for what the angle actually is. Instead you need to do something like in my build log - stick the dial indicator on one of the bearings and mount the straight edge parallel to the rail, but some distance (say 200mm) horizontally away from it. Make the indicator touch the straight edge, with it's movement perpendicular to the surface. That will convert the angular reading into a linear reading and amplify it. You don't need to worry too much about getting the straight edge level, as if you plot the readings on a graph that will just make a linear error which you can subtract.

Just out of interest, how much did the straight edge cost?

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I'm not too worried about the life of the bearings, as you say I'm sure it will outlive me and for what it's being used for. I will measure it though out of interest as I have the straight edge ...

The straight edge was from Axminster http://www.axminster.co.uk/veritas-a...-straight-edge it's got a claimed accuracy of 0.075mm over the 1270mm length which although not super accurate is more than good enough I think for my purposes.

Picking up Jonathan's comment re stiffness in roll and manufacturer's tolerance...

HiWin 20mm rails have a maximum permitted height difference of 0.130mm with 500mm rail spacing. That corresponds to a difference of 0.013mm across that 50mm or so bearing block. Don't know about you, but that's about a quarter of my thinnest feeler - and that's the maximum allowable tolerance. As for stiffness - and I don't recommend you do this at home as I only did it by accident - my gantry structure probably weighs around 30kg, and I managed to leave it hanging while only attached to the carriage at one end. It probably dropped by no more than 25mm or so. I hate to think of the abuse of the pair of bearing blocks taking the weight, but what's done is done. I shall be reporting on my experiments with epoxy (i.e. mistakes and how I've tried to correct them) elsewhere when I'm actually happy with the results, but in simple terms, it's a lot easier to get the rails level than to remove twist. The main reason to get the rails level (given that you will take out minor variations by machining the spoil board anyway) is that with, say, a 1000mm rail spacing, the max rail height difference spec only allow a height difference of about 0.26mm (10 thou). That's not too difficult with epoxy, and I would expect rather better with just a bit of care. But twist? As long as it is constant, then the gantry to bearing block joint can be shimmed/adjusted to suit but you only need a tiny amount of varying twist to go way out of spec. I'm still trying to get mine somewhere near acceptable. I'm using a sensitive level (0.02mm/m readings) to check.

It would be easy to say that the problem is that I'm chasing irrelevant numbers with tools that are working at their limit, except that a trial bolt-down of rails with gantry mounted gave clear signs of graunching bearings even when I was happy with levels. Suck-it-and-see tells me that there's something wrong.

Attachment 14403

These are the NSK specs on running parallelism....seems in theory I have about 16 microns for my 800mm spaced rails to play with....to be honest I think you can keep chasing numbers till you're red in the face and for a router that's going to be used for wood and plastics mostly with some aluminium then I'm not going to get my knickers in a twist about it.

I'm going to do a quick test as Jonathan did (I'm intreagued now) and then once the gantry is made bolt it to the carriages and see what they sound and feel like.

I bet you wonder how you ever managed without a straight edge now :glee:

Picked up the cut tooling plate just now....gantry build can start next week though first got to design and build a pantograph arm for putting in M6 UNC bolts and grease nipples into 1000 units we're currently assembling for a contract....oh, that's after I've finished machining a custom unit that's just been ordered. Work keeps getting in the way of playing!

Attachment 14438

Been drawing up the gantry in Geomagic 3D program today. Getting there, so far all the holes etc. line up!

Attachment 14477

Looks good software on their website, can't wait to get stuck into that aluminium plate eh !

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Originally Posted by EddyCurrent

Looks good software on their website, can't wait to get stuck into that aluminium plate eh !

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Yeah its good software, we just got the Mill package that goes with it so should be able to draw parts and then mill them on the router or the next project which is CNCing the mill...

No I can't wait to get stuck in. Taking my time making sure it can be put together etc...[emoji3]

I found that it could only be designed and drawn up to point, the rest was sorted out as it happened.

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Originally Posted by EddyCurrent

I found that it could only be designed and drawn up to point, the rest was sorted out as it happened.

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I think that's what's going to happen here. The major holes etc will be drawn and then the fine adjustments and fitting will be done ad hoc.

Hope to get it all machined up by mid next week in between the other bits of work I have to do.

Been working on the Z axis today, not done it all by any means as work keeps flipping geting in the way...

Attachment 14480

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Not drawn the plates that the Y axis Carriages attach to yet (simple so won't take long) ot the Z axis Stepper plate which is going to have a pocket for the stepper milled into it with slots so the belt can be tensioned. The Z carriages and rails are just blocks drawn to the correct dimensions but with no detail, couldn't be bothered and couldn't see the parts in the online library to download but not looked too hard!

Put some material back on that front plate it will help with resonance. You only need to remove what you need to remove for the screw to clear.

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Originally Posted by JAZZCNC

Put some material back on that front plate it will help with resonance. You only need to remove what you need to remove for the screw to clear.

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Cheers Dean, I'll alter that tomorrow.

Quick question. I was going to use the DIY spindle that I've made but seeing as I'm not paying ill probably get a water cooled spindle and VFD, now is it worth getting the 2kw or 3kw one and which VFD (without going overboard on cost that is!) to get and any recommendations where to get them?

Keep in mind this info is a bit over a year out of date but I got a 2.2kW water cooled spindle and VFD from Chai for £216 ex VAT. There were places that were a little cheaper but as I was getting other parts from Chai it made sense to get them all together. I also found a load of suppliers on ebay that I wouldn't touch with a barge pole, YMMV, worth a google pre-purchase though.

Front plate re-drawn with smaller pocket in it...

Attachment 14484

Dean, you did realise that the front plate is a 40mm thick plate? The pocket is 20.6mm deep so 19.4mm still remains in the middle.

Anyhow....managed to get another few minutes on the CAD....put together the assembly and surprisingly it all fits together!

Attachment 14485

One last pic before home time.....the Z axis on the gantry....

Attachment 14486

Not sure if this will work but I've just created a 3D PDF of the router which I'll try to attach...I know I've not done the 50x25 cross members yet...or put things like steppers, ballscrews etc but it's just the basic frame and gantry.

Attachment 14494

Opens OK in Foxit Reader
Mike

Well it worked for me. I didn't know PDF's could do that, I must investigate more. The rendering is as good as you get in something like SolidWorks. The design is looking good and really coming on a pace now.

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Originally Posted by mekanik

Opens OK in Foxit Reader
Mike

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Cheers Mike...

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Originally Posted by Wobblycogs

Well it worked for me. I didn't know PDF's could do that, I must investigate more. The rendering is as good as you get in something like SolidWorks.

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I've not played with the clours and rendering yet, will do if I get time. We've bought an add on that means you can make animations, can't wait to install that and have a play with it (bought it to do work animations for our new web site that we're currently designing)

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] The design is looking good and really coming on a pace now.

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Again cheers, just doing the dimensioned drawings for the pieces now so I can start the machining...looking forward to that!

Set up a straight edge parallel to the master rail 300mm away and put a DTI on a carriage and moved it up and down the rail. There's about 0.25mm of twist/dip mostly near the rear of the machine.

Only conclusion I can accurately draw however is that my DTI is too cheap as it moves all over the place i.e. doesn't return to zero after going up and down a few times...need a better quality DTI....

Did a bit of drawing as well today...

http://tapatalk.imageshack.com/v2/15...7ba3999032.jpg

Quote:

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Originally Posted by njhussey

Set up a straight edge parallel to the master rail 300mm away and put a DTI on a carriage and moved it up and down the rail. There's about 0.25mm of twist/dip mostly near the rear of the machine.

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Any thoughts on what might have caused this? I'm still experimenting with my machine and epoxy but it's been too cold in my garage lately to pour any more. Took the old epoxy off this afternoon and shall shortly be trying a slightly different technique.

Quote:

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Originally Posted by Neale

Any thoughts on what might have caused this? I'm still experimenting with my machine and epoxy but it's been too cold in my garage lately to pour any more. Took the old epoxy off this afternoon and shall shortly be trying a slightly different technique.

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I'm going to check the rail for bow/dip tomorrow with the straight edge to see if it's that. If it is then ill shim the rail where it's twisted if I can.

Looking at the rail today I put the straight edge on the rail and tried the feeler. There's a dip at both ends (last 6 inch) of the rail so ill have to shim that before carrying on much further :(

Not done much else on the machining as been making a tapping arm today...

http://tapatalk.imageshack.com/v2/15...d1bdfc9bba.jpg

Needed some 20mm aluminium for a clamp for the pantograph arm I'm making at work so put the big plate I've got on a table and used the Evolution circular saw to cut the plate to size for the bed. The 100mm strip cut off will be used for blocks for mounting the ballscrew mounts on etc...

http://tapatalk.imageshack.com/v2/15...777a7c7978.jpg

How well does that saw cut ? I used a sabre saw last time but you can't get a good straight line with it. I have a Hitachi saw similar to the one in your photo, I wonder if an evolution blade will fit ?

I was sceptical about the adverts for it but it cut a 1" steel bar and slowly munched through the Ali plate, my steering left a bit to be desired at the end but it's not critical as it's going on the base and all the blocks will be milled to size. Next time I'll use a fence to guide the saw rather than my eye ;)

I believe that Evolution have made the blade hole diameter different from mist blades so it can't fit any other saw....but don't quote me on that. I remember reading it somewhere, a forum or somewhere like that.

I cut 10mm aluminium plate on my mitre saw using a regular TCT cross-cut wood blade, just sprayed on a bit of WD40 before the cut. It was similar to cutting a very hard, close grain, wood except the aluminium was a little sticky feeling. I think a rip cutting blade would be better as it wouldn't stick so much as it cut. Anyway, I'd happily make cuts with a regular circular saw if didn't have a better option to hand, not sure I'd even go to the expense of getting a special blade unless I was going to do a lot of cuts.

I've been cutting 20mm Ali plate dry for years with and TCT thin kerf cross cut blade in table saw that is so knackerd it won't cut Oak without smoking the workshop but yet munches Ali no problem. Absolute must that you wear full face mask and cover arms and neck as the chips are scorching hot.!

yes tct blades cut ali with no problems as long as you take your time. Used one of these in the chop saw to ali http://www.ebay.co.uk/itm/250mm-Circ...item58b7e8d3eb at £9.50 I was a bit sceptical but it cut OK no good on wood as it burns and does not cut so well, like Dean said just fills the shop with smoke.

Been doing machining in between making a tapping/pantograph arm....arm's finished (minus cleaning and painting) and mounted on the wall ready for the next batch of units to come through the works.

Attachment 14639

Can't wait to get cracking on the rest of the machining and assembling the gantry.

Must start the contorl panel shortly too so will be looking through the threads and then asking lots of questions about PSU's etc......:stupid:

Got a few bits to assemble now, can't find the bolts I got for it so going to have to go out this afternoon and get some more :hopelessness:

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The Z Axis plates are still to be done as are the Y carriage mounts.

Should be able to get the second X Axis rail aligned using the gantry soon :beer:

Some more photos...

Attachment 14646 Attachment 14647 Attachment 14648 Attachment 14649 Attachment 14650 Attachment 14651 Attachment 14652

Squared up the X Axis carriage with the DTI...

http://youtu.be/RmBQaucbpiQ

Found out that the frame that started out nice and square over a year ago (when I welded it) isn't actually square anymore....there is 2 or 3mm of rail sticking out the left side when the right side (depending on your viewpoint of course) is right at the end.....(edit: just measured it and the rail, which is not bolted down yet, had moved back a bit!!) nothing drastic, just annoying.....

http://tapatalk.imageshack.com/v2/15...aabe23e4d9.jpg

Second rail is squared up and drilled, tapped and bolted down. I can't notice any tight spits but as Jonathan said you've got to really get them out of line to notice any tight spots.

Tapped the holes on the top of the gantry and used the straight edge and DTI to get it as near straight as possible.

https://www.youtube.com/watch?v=6Jug438XMd4&list=UUX_ImztPc6hUkKDfklSSdBA

Just going to do the same for the bottom rail....

Edit: The DTI is running along the front if the aluminum plate not the rail itself...

Painting the frame tomorrow...