Here we go again . . . MK4

Cheers guys thanks for the encouragement. The end seems along way off still. Vice is precision vice from ArcEuro trade. About £100 - really nice would recommend it. Can use as an angle plate to square up against parts as all sides are ground

Link to the vice:
http://www.arceurotrade.co.uk/Catalo...l-Vices-Type-2

130-040-02000, Precision Tool Vice Type 2 - 90mm wide

£104.24 inc VAT

"Looking very nice ad sturdy.

This is how I got my beams sorted I welded 15mm plates on each end and then had them machined parallel and to length. I also had two faces of the box machined to get the box section true so that the front plate could be bolted to the beams true"


How did you do it Clive? Asking as this should be done in one operation/clamping - long piece.
Thanks

Quote:

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Originally Posted by routercnc

As I feared the return to work after Christmas means workshop time has significantly reduced. For various reasons I've only been able to get about an hour in there.

But I have been able to get a few sessions on the CAD and this has meant I was able to go over some of the other designs and have one last go at unlocking some of the compromises. The net result is I've developed some of the other ideas and ended up with what I think is a much better design.

Old one for comparison:
Attachment 17242

Here is the new version:
iso
Attachment 17235
iso rear
Attachment 17236
X axis
Attachment 17237
Y axis
Attachment 17238
Z axis
Attachment 17239
Just X axis showing gantry, ballscrews, epoxy (orange), and custom ballscrew floating end as the ballscrews were not long enough to mount the standard floating end.
Attachment 17240
X axis drive and belt tensioning arrangement
Attachment 17243
Side View:
Attachment 17244

The new features are:
Gantry beams smaller
They are now 80x40x5 RHS steel (down from 100x60x5). I'd put too much emphasis on huge sections, whereas with a double beam gantry I could afford to scale them down and still have plenty of stiffness in reserve over a single gantry.
Because they are smaller I was able to re-configure the X-bearings, bring them closer together, and give more travel in X. They are now only 274mm apart which is getting close to my current machine spacing. I was also able to get the X ballnuts at the centre of stiffness, rather than at the ends of the gantry.

Y rails are much lower
With the smaller gantry sections the Y rails are now lower and closer to the tool, as are the Y axis bearings, which all provides more stiffness

Ballscrews lower
As the gantry sections are narrower I was much happier putting the ballscrews on the front and rear faces as there was much less of a bracket required to join them back to the main Y axis, therefore stiffer.
These are now much lower in Z which also puts them much closer to the tool, which reduces the moments, which lowers the forces on the Y bearings and makes the machine stiffer.
I was also able to put the ballnut in the centre of stiffness, rather than on the outer edge of the Y axis. There might be a marginal gain here I really don't know, but it does look nicer.

Y axis bearings spacing
By re-designing the gantry end plates to free up some space I was able to make full use of the linear rail and spread the Y axis bearings out considerably more than before - without losing travel. This should significantly improve the stiffness due to moment inputs when cutting in the Y direction. When coupled with the lower ballscrews there should be a double win here.
In one of my earlier posts I suggested that double ballscrew on Y eliminates racking - whilst this is true for rotations about Z axis, it is not for rotations about the X axis. To eliminate these you could add another 2 ballscrews lower down, but that is not practical (!) so you do still need to space the Y bearings out even with double Y ballscrews. Rotations about the Y axis are dealt with by having the double gantry beams no worries there.

X drive
I've gone with something a bit different here which does not use tensioning idlers. The steppers are on plates which are slotted, and the steppers are also in slots. Between them I should be able to tension the short belt up to the ballscrew, and the syncronising belt across to the other stepper at the same time by pushing the motor off into one corner. Everything is 5 HTD with 15mm belts.

Cooling
I've decided that there are a couple of options to place the radiator, plus the option just to go for the 'big metal bucket' out of sight. So I'm going to build it and then just see which one takes my fancy. Sometimes you can CAD things too much and get tied up in the last details.


Luckily the new design retains the parts I'd already made so nothing lost. Thank you for the comments made so far, stirring up the doubts I had about some aspects, and making me revisit the previous designs. I think it is all the better for it.

Right, time to start CAMing up some of the parts ready for whenever the next workshop session is . . .

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Attachment 20092Attachment 20093Attachment 20094


Amazing project - can not wait till is finished
I had similar idea how to drive two ballscrews

Quote:

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Originally Posted by Tom J

"Looking very nice ad sturdy.

This is how I got my beams sorted I welded 15mm plates on each end and then had them machined parallel and to length. I also had two faces of the box machined to get the box section true so that the front plate could be bolted to the beams true"


How did you do it Clive? Asking as this should be done in one operation/clamping - long piece.
Thanks

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They were done on a Hurco VMC clamped and machined in one operation ie front and top faces machined and both ends. But I had to take the two beams to a guy with a horizontal mill to get the holes in the ends drilled and tapped.

Then the front gantry plate was bolted to the machined faces of the 60x60x5 box.
It was the only way I could make sure that the gantry would be square and true.

The drilling at tapping cost me about £25 for the 16 holes.

Quote:

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Originally Posted by Clive S

They were done on a Hurco VMC clamped and machined in one operation ie front and top faces machined and both ends. But I had to take the two beams to a guy with a horizontal mill to get the holes in the ends drilled and tapped.

Then the front gantry plate was bolted to the machined faces of the 60x60x5 box.
It was the only way I could make sure that the gantry would be square and true.

The drilling at tapping cost me about £25 for the 16 holes.

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Very good price Clive, where was it?
For profile up to 50mm I use lathe with independent jaws.
All the machine I have access to are limited with size (sort of big model engineering)

Quote:

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Very good price Clive, where was it?

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It was done by local engineering firm as a job on the side by the boss in Stockport.

Thanks Tom. Yes, lots of ways to drive 2 ballscrews - that one would work as well.

Your little machine looks really good. Nicely built !

OK, more updates. To finish off the info on the bed rail supports, here is the little jig I made up to hold the bosses in place:
Attachment 20182

Here it is in position:
Attachment 20183

It uses 6mm shoulder bolts to give a good reference position and picks up off the inner tapped hole already there. This holds the boss in just the right place for welding. It's now ready for welding - just need to catch my friend with the welder in the next few days or so. This is bolt down the supported rail which obviously uses a pair of bolts on either side of the flange.
I've also taken the opportunity to spot out the holes for a profiled rail (i.e down the middle) to make a future upgrade much easier to do.


Next up are the end plates which hold the motor mounting plates. Starting with a nice skimmed off the sacrificial board:
Attachment 20184

Then setting up:
Attachment 20185
(note that I've scribbled down the X, Y, Z coord of the workoffset on the drawing - I always write them down in case of power failure)

I'm making a mirrored pair here. A few holes, and a large pocket in the middle of each one. You can drill and screw through the waste first, but and I'll talk you through my approach on the large cutout as it worked quite well as an alternative. This is all to avoid those terrible tool witness marks from tabs.

1) Use an inside profile with a 1mm offset (remaining stock on the side wall) WITH TABS.
Attachment 20205

2) Then drill through the tabs with a cordless drill to remove the waste:
Attachment 20187

3) Manually jog the machine to remove most of the tabs (not critical to get all of it)
Attachment 20188

4) Clean up profile pass to remove the last 1mm. I do this in 2 stages as this is what works for my machine. 1st cleanup 3mm DOC, 0.9mm WOC, final cut full DOC, 0.1mm WOC.

Gives this surface finish:
Attachment 20189

Then bolting down, removing clamps, and onto the profile cut:
Attachment 20190

Same approach as above using a rough cut leaving 1mm stock, then semi-finish 3mm DOC, 0.9mm WOC, and finish full DOC, 0.1mm WOC. A stiffer/better machine might do the finish in one pass. I'm also limited to 6mm max cutter on ER11 collet. Good finish anyway:
Attachment 20191

Mirror part cut the same way, then some holes tapped and surface cleaned up:
Attachment 20192

The bearing end plates were done in the same way:
Attachment 20193

Then onto the bearing holders:
Attachment 20194

Attachment 20195

They will be a light press fit:
Attachment 20196

Second one made:
Attachment 20197

Trial fit onto the bearing plates:
Attachment 20198

This allows the ballscrew end bearing position to be fine tuned when setting up.
__________________

Moving away from the X axis and onto the Y axis - the belt tensioning system progresses. Turned some standoffs to hold the adjustable belt guide bearings:
Attachment 20199

Attachment 20200
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Looking ahead I need to turn down the end of one of the ballscrews. Made these 2 bits to hold it in the lathe. First is a protective collar to stop the jaws damaging the ballscrew:
Attachment 20201

Made it by boring a hole into some round stock on the lathe.
Then machined a hex onto some round stock:
Attachment 20202

Then used the hex to give 120 degree spacing to machine the 3 slots. Don't have a hex collet block which would have done the job!
Attachment 20208

Then back to the lathe to part it off:
Attachment 20203

Then to support the end of the ballscrew as it passed out of the headstock a spider/collar to fit inside the lathe spindle bore and hold the ballscrew. The ballnut is then 'tightened' up against it. Copied the whole idea off Youtube so should be OK!
Attachment 20204

Maybe by mark 4 I'll be this good - v nice


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