X and Z mods

discussion of design changes / improvements / suggestions
microwavesafe
Posts: 48
Joined: Mon Apr 09, 2012 5:47 pm

X and Z mods

Post by microwavesafe » Mon Feb 11, 2013 5:42 pm

I wanted to mod the X axis to improve the flex and more comfortably cut aluminium stock. This was always going to take the form of double X rails, but I wasn't convinced you could eliminate the flex with the delrin V wheels. So when I discovered that Bart had some metal V wheels which incorporated the bearings I knew what I wanted to try. Problem was they would ruin the maker slide and they were a different size. So I bought into the kick starter on the Open Rail as this was hard coat anodized. Fast forward 6 months!

I drilled holes in the standard plate and the X axis steel plate, to take into account the smaller size of the bearings. I used M5 x 30mm threaded spacers so I could tighten the screws in from both sides and increase the mechanical coupling between both plates. I bought a peice of 40 x 40 aluminium extrusion, and mounted the open rail on all four sides and fitted the new X axis assembly.
X axis 1.jpg
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This effectively eliminated any flex on the X axis, but there was some flex left in the Z axis. This was caused by the standard plate bowing out between the V wheel supports allowing the V wheels to spread slightly.
Z axis 1.jpg
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Luckily I had another standard plate and two more eccentric nuts to hand. I copied the new metal V wheel mounting holes, but I also drilled a middle hole to add a third pair of delrin V wheels against the Z axis maker slide. Adding the second plate prevents bowing in the plate and a third set of V wheels helps spread the load across the plate better. The middle pair are both on eccentric nuts so they can be tightened against the Z axis.
X and Z 1.jpg
X and Z 1.jpg (57.74 KiB) Viewed 4933 times

microwavesafe
Posts: 48
Joined: Mon Apr 09, 2012 5:47 pm

Re: X and Z mods

Post by microwavesafe » Mon Feb 11, 2013 5:46 pm

With all these mods in place the Z axis flex at the cutter is massively reduced. I can post hole placement information if anyone is interested.
I'd quite like to use the new set up to cut a new Z axis plate as I believe I will get more strength out of a single piece of 6mm aluminium, as opposed to two strapped together?

Anyway a couple more shots of the complete mod.
Complete 1.jpg
Complete 1.jpg (62.74 KiB) Viewed 4932 times
Complete 2.jpg
Complete 2.jpg (73.78 KiB) Viewed 4932 times

Improbable Construct
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Location: Fairhope, AL
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Re: X and Z mods

Post by Improbable Construct » Mon Feb 11, 2013 7:22 pm

Nice work!

I have some Open Rail on order as well. It was supposed to be here on the 7th but the post office seems to have lost it!
I tried the two standard plate arrangement at one point as well but i didn't think that it did much, so I abandoned the idea.
I do think that one thicker plate would work much better than the two stuck together.

I ordered some of the Open Rail steel wheels and am anxious to see how they work out.

The extra v wheels on the Z axis is an interesting idea. Good thinking on putting them on eccentric spacers.
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bvz2000
Posts: 1
Joined: Mon Feb 11, 2013 7:41 pm

Re: X and Z mods

Post by bvz2000 » Mon Feb 11, 2013 7:50 pm

Wow, I love your machine!

I am just about to order the full kit and am looking forward to modifying it as much as I am in creating things with it. Your post (among many others) is a real inspiration. I have been lurking around cnczone for about three years now and have about 100 sketchup designs for my own cnc setup that I never every had the time to dig into. Now with shapeoko I have a place to start.

Keep up the good work.

microwavesafe
Posts: 48
Joined: Mon Apr 09, 2012 5:47 pm

Re: X and Z mods

Post by microwavesafe » Mon Feb 11, 2013 8:08 pm

@improbable

I put a bolt through all the spare holes as well so the plates couldn't flex much. It did help, with the strong coupling to the steel plate. I've thought of a better idea while I was writing this up though. The main bowing point is between the two spacers, there are two 5mm holes at the bottom in the middle of the standard plate. I'm going to drill these through the steel plate and put M5 x 50mm threaded spacers in. This will provide support in exactly the right place.

@bvz2000

I completely agree with you! I have always wanted to build my own cnc, but with so much information I didn't know where to start. The ShapeOko is an excellent place to start. It works straight out of the box and can be extensively modified due to it's open source nature. Modifying it is as much fun as using it!

PsyKo
Posts: 430
Joined: Thu Aug 30, 2012 8:42 pm
Location: France

Re: X and Z mods

Post by PsyKo » Tue Feb 12, 2013 9:30 am

Microwafesafe that's a nice machine you got here.
Did you had a chance to "measure" the flex you have in the Z axis before and after those mod ?

I'm also interested for further information about the open rail and steel wheel performances.
Keep us informed. Thanks
Shapeoko #736
Kress 800, Z Axis upgrade, dual Y, 600mm X&Y rails, metal spacers and V Wheels, home switches, 4th axis
Goko - Free CNC Control Software - http://www.shapeoko.com/forum/viewtopic ... 380#p44380

microwavesafe
Posts: 48
Joined: Mon Apr 09, 2012 5:47 pm

Re: X and Z mods

Post by microwavesafe » Tue Feb 12, 2013 11:29 am

Ah measuring you say!

I didn't do anything other than laying down a ruler, but before the mod I could get 2 to 3 mm flex at the end of the cutter at maximum extension. There seemed to be a point where the bearings inside the V wheels on the X axis would 'click' and give another mm or so. I believe this has been mentioned before where the precision shim isn't fitting perfectly between the two bearings so the delrin can slide slightly.

After the mods at full extension and pushing as hard as I can (the same as before, but I haven't got a force meter so I can't be 100%!) the flex is down to 0.8mm. Not particularly scientific, but enough to convince me that it's worth it.

I should point out that the bearings are this type http://store.makerslide.com/index.php?m ... ucts_id=75 . Not the Open Rail steel wheels. The Open Rail steel wheels follow the same design as the delrin and to my mind will suffer from the same tolerance issues. The RM1ZZ V groove bearings have integrated bearings with a single piece bore hole so you can tighten right down on them without causing them to bind. They are designed for high axial loads and perform very well in this application. Not saying the Open rail ones wont! I just haven't used them so I can't say.

The nuts with nylon inserts are a nice touch with the Open Rail delrin wheels, it stops the nut loosening when you adjust the eccentric spacers. I'm moving them all over to nylon insert nuts now.

I'm going to wait until I have some M5 x 50mm threaded spacers fitted between the standard and X axis plates, before I start cutting some aluminium. I will let you know if the reduction in flex translates to better performance.

microwavesafe
Posts: 48
Joined: Mon Apr 09, 2012 5:47 pm

Re: X and Z mods

Post by microwavesafe » Tue Feb 12, 2013 1:27 pm

I also want to say that before the mod a small force could flex the Z axis, with the mod I have to push quite hard before it even starts to move, so hopefully the cut wont exert this much force and the Z axis will remain constant.

I just wanted to quantify the results a bit, as simply stating the maximum flex values doesn't give a clear picture. Ideally I'd have a force to displacement graph for before and after, but that simply isn't going to happen!

PsyKo
Posts: 430
Joined: Thu Aug 30, 2012 8:42 pm
Location: France

Re: X and Z mods

Post by PsyKo » Tue Feb 12, 2013 2:36 pm

microwavesafe wrote:I also want to say that before the mod a small force could flex the Z axis, with the mod I have to push quite hard before it even starts to move, so hopefully the cut wont exert this much force and the Z axis will remain constant.

I just wanted to quantify the results a bit, as simply stating the maximum flex values doesn't give a clear picture. Ideally I'd have a force to displacement graph for before and after, but that simply isn't going to happen!
That's some good news.
I'll proably try and use those wheels on the makerslide rails. If they get worned too fast, I'll switch them.
Shapeoko #736
Kress 800, Z Axis upgrade, dual Y, 600mm X&Y rails, metal spacers and V Wheels, home switches, 4th axis
Goko - Free CNC Control Software - http://www.shapeoko.com/forum/viewtopic ... 380#p44380

microwavesafe
Posts: 48
Joined: Mon Apr 09, 2012 5:47 pm

Re: X and Z mods

Post by microwavesafe » Thu Feb 14, 2013 10:19 am

I've now fitted two 50mm spacers at the bottom of the X axis.
Bottom bracing 1.jpg
Bottom bracing 1.jpg (53.78 KiB) Viewed 4769 times
Unfortunately the local fastenings trade counter didn't have any 50mm M5 threaded in stock. So i've ended up with some aluminium tubing cut to size and bolted through with M5 75mm socket cap screws. This has again improved the maximum flex. It's getting hard to measure, but it's definitely less than 0.5mm, so it's probably been halved to 0.4mm. Again this is maximum flex at full force (although I'm not very strong!). Smaller force produces no measurable deflection.

Next step is to try this out on some aluminium stock and see if the flex improvements actually make a difference.

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