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  #1  
Old Mon 23 January 2006, 10:00
Dirk Hazeleger
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Linear bearing Z slide

Gerald
I Love your Z Axis. I was going to use 2 of the same style rails with 4 bearing blocks on the Z for the Mega bot. I like your design much better.
Dirk
What size rail are you using?
  #2  
Old Mon 23 January 2006, 10:32
Gerald_D
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I've had 2 linear rails (about 5' each) with 4 "runners" lying in my store for about 5 years. Recently, one rail got a bit shorter and a "runner" disappeared. This is what is left in the store:


It was a sin to cut it for a simple Z-application The rail is about 45mm square - nothing to adjust.

Yes, that is a gas spring as a counterbablance. I had the spring charged to 15kg (33lbs).

The support board is the standard size of our board material around here: 2750mm x 1830mm (9'x6'. The spindle axis has about 50mm extra movement on all four sides.
  #3  
Old Mon 23 January 2006, 14:08
dvanr
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Gerald,

Very nice design, I like the x-rails, flip around with the flange in, doesn't really matter how wide your steel flanges are locally the guide rail will always fit.

How did you level the guide rails? they look like they sit flat , with no washers underneath. Did you grind the guides once they were mounted? How did you grind them? You commented that your local guy didn't have a machine big enough.

I really like the Z-axis design you came up with , gas strut in particular. I have been trying to come up with an alternate Z-axis design too and now wonder if linear bearings on two parallel 16mm round bars would be strong enough. (I see that your slide is way larger than that) Should I be looking at larger THK slides instead?

ps, waiting for my activation key
  #4  
Old Mon 23 January 2006, 22:21
Gerald_D
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There are shims under the x-rails - max of 0.6mm thick. I still have a scheme to re-grind the rails in place, but the first priority is to de-bug the machine for coarse errors. (It is probably going to spend most of its life cutting décor for window displays and fine tolerances are not required for that)

My gut feel is that 2x16mm round bars are too light. If you want 150mm of z-travel, and you want bearings 120mm apart (footprint), then those bars must be a minimum of 270mm long, only supported at their ends. That is the snag with round bars, they are typically end-supported only.

This would have been my choice of slide......


.......if I didn't die of a heart attack after hearing the price! (Two carriages and one rail)

Anybody notice the "sideways" z-motor? That is to leave a huge hole through the y-car for the dust extractor pipe.
  #5  
Old Mon 23 January 2006, 23:24
dvanr
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hmmm..

I was hoping to use the typical ballscrew z slide idea. Like the early PRT series. My thought was, there are two sides to a Z slide and plenty of room in the Y-car opening. The router fixed as usual and a drill on the other side. The one Z motor would control both. The drill would be retracted out of the way on a 6" pneumatic slide. When required air would send it down a couple of inchs past the router bit, normal Z motion would then do the drilling.
  #6  
Old Thu 26 January 2006, 01:00
Gerald_D
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Dick, the drill doesn't need as strong a support as the router - little side force on the drill. If I were to mount a drill on the back of my slide (in place of the dust hose), I could hang it off the top and bottom ends of the rail, thus "bridging" over the carriage block. In fact, that is how I plan to carry the dust hose.
  #7  
Old Thu 26 January 2006, 04:42
Dick van Randen
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Gerald

Yes, that would work really well. I got stuck in the rut of the usual end mounted Z stepper in the ball screw style axis.(that creates a whole new set of problems mixing rack and pinion with screw speed ratios) Had only briefly thought of side mounting the motor. I am liking the possibilities of your design more and more. ( I am also now thinking about redesigning my current router bracket with a bridge over the router to mount a drill with a positioning slide.)
  #8  
Old Fri 03 March 2006, 18:36
Harold Weber
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The gas spring sounds like a good idea. I found this web site
http://www.easylift.com/e-tecinfo2.htm
that discusses how gas springs work. They mention a "scraper" option which can be used to remove sawdust.
They also mention service life of 50000 to 70000 cycles. Not sure how that would apply; I'm thinking that I could get a couple of thousand 10 mm movements up and down while cutting some 3D parts. Would not be using the full stroke very often though...
  #9  
Old Thu 21 September 2006, 10:17
Sheldon Dingwall
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Gerald, How is your linear bearing Z slide working out? I was surprised to see you use a single slide as it seems like the router would apply a substantial tortional load on the single slide. Other than that, it looks like a pretty elegant solution.
  #10  
Old Mon 02 October 2006, 07:02
Gerald_D
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That slide is working great. But remember that it is a quite a big size.
  #11  
Old Mon 02 October 2006, 09:49
Sheldon Dingwall
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Thanks Gerald.
  #12  
Old Mon 02 October 2006, 22:52
Gerald_D
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The following pics were posted 22nd January 2006 in another thread:






  #13  
Old Wed 01 November 2006, 02:21
Gerald_D
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A pair of INA KUVE30-W's is looking quite attractive to replace the huge linear bearing I used before. In other words, still one rail TKVD30-W, wider and flatter, but two shorter carriage blocks, one above the other. They are stocked in this country and I can get the whole setup for under $500. (Your prices may be quite different - I buy a lot from this supplier and get good discounts)

A single carriage block could very well be sufficient. Will have to order some and test them out.......

And the plastic plugs KA15-TN/A shall not be forgotten....as I notice that most rail users do. Those plugs give a smooth surface for the seals to wipe over the screw-heads in the rail.
  #14  
Old Wed 01 November 2006, 03:33
Gerald_D
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  #15  
Old Wed 01 November 2006, 05:14
Mike Richards
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Gerald,

If I've read your post correctly, you're suggesting that we use a single rail with two sliding blocks for the Z-axis. Did I understand your post correctly?
  #16  
Old Wed 01 November 2006, 05:15
Gerald_D
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Also considering a pair of KUVE25-B-KT-W's. They are in the catalogue, but not in the country.....
  #17  
Old Wed 01 November 2006, 05:23
Gerald_D
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Hi Mike

At the moment I am using a single block and single 45mmWide rail and it is working very well. But it is a long (heavy) block and narrowish rail. A wider rail will be better, and I think two short blocks instead of one long one.

Most of the selection is going to hinge on costs and availability. But I am taking a very conservative approach now and the drawings replicate what is in the already working MechMate. My snag is, the rail I used so far has no markings and I have no data on it. I lean to INA bearings because we use them a lot in my dayjob, albeit not for linear bearings.
  #18  
Old Thu 02 November 2006, 01:21
Gerald_D
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So the delivery guy has just tried to deliver me KWVE30 instead of KUVE30-W - they are so used to dealing with KWVE that they thought I was making a mistake in my order! The price above is obviously wrong now.
  #19  
Old Thu 02 November 2006, 08:14
Sheldon Dingwall
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Just currious, there seem to be a lot of used smaller rails and blocks on ebay and elsewhere. Would two smaller rails and 4 blocks work as well?
  #20  
Old Thu 02 November 2006, 09:07
Gerald_D
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Sure they would work in principle, but my snag is to publish a drawing where someone can buy model xyx from supplier abc and the whole thing will simply just screw together. I am trying to findly an affordable and universally accessable solution. Technically, the "Wide" INA bearings are a perfect solution......


.....and their sales office got my hopes up yesterday that the price was right too. Now I am back to square one.

Can anyone price the INA KUVE25-W or KUVE30-W bearings out there? The "W" is for wide - with 2 rows of screw holes in the track. Tracks must be over about 60mm wide and only about 20mm high. Anybody know of other brands?
  #21  
Old Thu 02 November 2006, 09:23
Dirk Hazeleger
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Here's one that might work. Don't know the price but other quotes I recieved were reasonable.
http://www.hiwin.com/lg/mg.html
Dirk

Edited:
After looking some more the rails may be smaller than you like
  #22  
Old Thu 02 November 2006, 09:58
Gerald_D
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Thanks Dirk. A 42x16 mono-rail may *just* be passable, seeing that I am doing fine with a rail only 45mm wide now.......
  #23  
Old Thu 02 November 2006, 10:21
Gerald_D
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The LWFF69 from IKO is also technically fine.
  #24  
Old Fri 03 November 2006, 01:15
Gerald_D
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The IKO LWFF69 bearings are stocked here. Price for one "carriage" and 0.5 meter of rail is around $1200 !!!! Time for plan B.....
  #25  
Old Fri 03 November 2006, 06:57
Mike Richards
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Gerald,
Hi-Win has some large blocks and rails that aren't too expensive. The HGW55CCZ0H block is $137.24 and 1/2-meter of railing is $159.37. (Prices are from www.hiwin.com)

The basic dimensions of the block are:
Width = 116mm
Length = 165.7mm or 203.8mm
Height = 70mm
Weight = 4.52kg or 5.96kg

The rail:
Width = 53mm
Height = 44mm
Weight = 15.08 kg/meter
  #26  
Old Fri 03 November 2006, 08:01
Gerald_D
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Hi Mike, I am at home on slow dial-up at the moment so I can't connect to hiwin, but that appears to be a more common rail profile - nearly square (53 x 44mm). The prices for these are okay'ish and they will work, as per the first MechMate pictured right at the top of this thread. But, it is a very heavy solution at about 10kg [22lbs].

Also, the more I dug around on linear rails, the more I realised how little I know about them and how complicated they can get. (That's aside from the price run around from supposedly reputable dealers). The IKO literature was the only place giving me pre-load options, and for a single carriage on a single rail we want pre-load (ie. no chance of backlash). The dealer couldn't tell me if those he had in stock had pre-load or backlash - nobody had asked him before. The rails I used appear to have pre-load as well. My dilemna now is give plans with linear rails and then a user gets rail with no pre-load...... So, I thought it best just to walk away from linear rails all together, particularly since I am not advocating them in the x and y rails either. There are just too many variables beyond our control.
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