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  #1  
Old Fri 03 November 2006, 02:09
Gerald_D
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Flat Plate fabricated slide

After finding that linear bearings are exhorbitantly expensive, plan B.....

"Gauge Plate" is very precise, high-quality, slightly hard tool steel that can be hardened even further. Running pre-loaded big V-rollers on this stuff should work okay.

Typical standard sizes./. More

Thinking of a 6mm x 100mm plate, ground as per the pics in this thread and screwing a backing/stiffener to it.
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  #2  
Old Fri 03 November 2006, 06:00
Gerald_D
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Yellow is the hard plate with a green 50x25x3mm [2x1x.125"] tube screwed to it. Rollers BWC size 3. For this route, I'd ask to spindle maker to put more tapped holes in the top end of the spindle - that would add a lot of stiffness to the assembly. (I will drill and tap the spindles here already).
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  #3  
Old Fri 03 November 2006, 07:48
Brian Backner
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For those stateside, you might consider Starrett precision ground oil hardening flat stock (tool steel). It would need to be ground to shape, i.e., it can't be milled, but it has the advantage of tremendous strength, very precise tolerances (typically 0.0001"/ft) and is widely available.

A good outlet is WT Tool (www.wttool.com):

1/4" x 4" x 18" is $42

http://www.wttool.com/product-exec/product_id/10206

1/4" x 4" x 36" is $85

http://www.wttool.com/product-exec/product_id/10394

They have many additional cross sections available.

Brian
Walpole, MA
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  #4  
Old Fri 03 November 2006, 08:40
Gerald_D
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Hi Brian, I think that is the same stuff that I am talking about, but we don't have big problems milling/drilling/tapping it?? Sure, at 230 Brinell it is harder/tougher than "mild steel" which is around 120. (If memory serves me right).

Your prices match those over here.
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  #5  
Old Fri 03 November 2006, 12:22
Sheldon Dingwall
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By the time you pay for the material and modifications, would it not be easier/cheaper to just buy BWC rail?
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  #6  
Old Fri 03 November 2006, 14:49
Brian Backner
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Gerald,

You are right about the oil hardening stock being machinable; in my post above, I was thinking of the high carbon air hardening steels - while they're still machinable, barely, they are much more unforgiving of tooling. I've typically had this stuff precision ground.
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  #7  
Old Sat 04 November 2006, 00:17
Gerald_D
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Sheldon, that is a typical view of the BWC rails, but it is not that easy....

BWC rails have a nice edge, but they are actually very flexible and flimsy. (a size 2 track is only 16x6mm [5/8x1/4"] overall) You still have to drill a lot of holes in them to screw them to a firm base. And then they end up being only as straight as the base that they are screwed to.


My logic is to put the V-edge directly onto the "firm base" if we have to go to trouble of making the base fairly precise. It saves a lot of drilled holes. (My Hepco literature avoids recommending screw sizes/spacings).

It is not that difficult to put a passable V-edge onto a short flat bar for the z-slide. We might not end up with something as "precise"(?) as BWC but it is going to be simpler, cheaper and still do a great job. And, if we work around a "flat bar" design, people can still easily add BWC rails to it. The basic "gauge plate" tool steel used all over the world is the perfect stuff for screwing BWC/Hepco rails to.
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  #8  
Old Sat 04 November 2006, 15:45
Sheldon Dingwall
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I was thinking of their double edge flat slide. It's available up to 76 mm wide.
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  #9  
Old Sun 05 November 2006, 00:40
Gerald_D
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How thick is it? The 76 direction is probably adequate, but I guess it is going to need something more to stop it from bending in the x-direction, or from twisting when you take a heavy y-cut. Price?
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  #10  
Old Sun 05 November 2006, 11:28
ralph hampton
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Sounds like Hepco GV3:
http://www.hepcomotion.com/db_pages/...=0001&cat=comp
They are the UK link to bwc.

R/
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  #11  
Old Sun 05 November 2006, 16:05
Sheldon Dingwall
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I was thinking flat re-inforced by your tube idea. They spacer slide is thicker - 19 mm I believe. But probably not thick enough.

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  #12  
Old Sun 05 November 2006, 22:53
Gerald_D
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If you reinforce the thin plate with a backing tube that should work fine. Just remember that the plate should be soft enough so that you can drill it.

A side note: Hardening of steel does not make it any "stiffer". For this slide application, the hardening is solely to improve wear resistance.
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  #13  
Old Tue 07 November 2006, 09:45
Gerald_D
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Here is some progress this afternoon:





The grinding in the table saw was surprisingly easy (20 minutes) A 175mm wheel protruding 26mm above the table surface gave the 2x45 degrees, albeit very slightly concave. Then some draw filing with a fine file and a bit of emery stone (20 minutes). There is scope for refining this process, but already the results are an A-class "pass".

If I had to do a lot of these, I would use a thicker(wider face) stone of a finer grit, but the 3mm thin cutting disc (coarse) was not too bad. The biggest job was to make a centralising bush for the disc in the table-saw.

Can I suggest you guys try it with any old piece of flat bar before you believe me?
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  #14  
Old Tue 07 November 2006, 14:11
Gerald_D
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I drilled some holes in that plate tonight. It sure is much harder than mild steel, but not impossible to work with. (Some stainless steels are much worse)

(The stockist of those $1200 linear IKO bearings came to me with a $500 price today. I think he is trying to move dead stock.)

the grinding discussion moved back to here
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  #15  
Old Wed 08 November 2006, 10:04
Gerald_D
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A rough assembly.......

(the big hole in the tube is for this quick change system)
Those 4 screwheads seen above are of screws going all the way through into the spindle's alu body. (2 long (shiny heads) and 2 short (black heads))

The countersunk screws above are tapped into the 3mm [1/8"] wall of the rectangular tube. Some extra holes in case positions need to be adjusted (and to see how long the tooling lasted while cutting the gauge plate - no problems)
The cut-away of the rect. tube is for the dust hose. The screws into the spindle body are near the collet end. I am tempted to drill+tap the spindle body near the top end for more screws - the spindle body is a nice flat, strong extrusion.
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  #16  
Old Wed 15 November 2006, 12:32
Gerald_D
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The eccentric bushings and rollers for the z-slide:


The eccentric bushes are modified bolts (drawing will be provided). Unlike BWC/Hepco, these bushings and support collars are relieved to avoid contact with the seals.




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  #17  
Old Fri 17 November 2006, 09:13
Gerald_D
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Some progress:



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  #18  
Old Fri 17 November 2006, 11:20
Evan Curtis
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paraphrasing Tony the Tiger "It look's GGGRRREAT!
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  #19  
Old Fri 17 November 2006, 12:50
Gerald_D
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Thanks Evan, that encouragement earns you one more pic:

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  #20  
Old Sun 19 November 2006, 05:35
Gerald_D
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The weekend's work - first prototype fully assembled (almost):










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  #21  
Old Sun 19 November 2006, 18:52
Robert Cheal
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It looks awesome and very well thought out.

Just curious what is the expected life on the "Gaslift". And also is it difficult to get the correct tolerances on the mounting holes after the bracket has been bent into shape. I guess a good shop could bend it right the first time.
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  #22  
Old Sun 19 November 2006, 22:59
Gerald_D
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Hi Robert. The matching holes in the Y-car are oversize and slotted. (You also need the slotting for adjusting the Z perpendicular to the table.) This "tower" will not work in a ShopBot y-car because that car can't support the 4 legs of the "spider" firmly. With the stiff car of the MechMate, the four attachment points of the spider are slightly flexible so that they can conform to the car. The stiffness of the y-car is used directly behind the V-rollers.

I don't know the life expectancy of a gas-lift in this application. We have nearly run one year with the first one and so far, so good. However, I will design a conventional spring system as well - anybody have a skyhook to hold the top end of a spring?

(apologies for the home welding quality on those nuts)
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  #23  
Old Mon 20 November 2006, 00:42
Alan Conolly
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Hi Gerald

Very neat design - n boer maak n plan!

How do you maintain pressure on the pinion gear to hold it into the rack, or will that become apparent once it is mounted into the Y car?
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  #24  
Old Mon 20 November 2006, 00:58
Gerald_D
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Hi Alan. You can see a capscrew sitting next to the motor on the motor-mounting plate. A spring is hooked around it and the other end of the spring goes down to the Y-car. Same as the situation with the current linear bearing version:


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  #25  
Old Mon 20 November 2006, 08:16
Dirk Hazeleger
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Hey Gerald
I noticed the motor on the new Z your using direct drive. Is that what your planning on? What are your thoughts as to direct drive vs geared motors for all axis.
Dirk
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  #26  
Old Mon 20 November 2006, 08:46
Gerald_D
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Hi Dirk, my suggestions on motor selection are in this thread. However, that thread actually applies more to the x and y axes than the z. We must recognise that the demands on the z-axis are a bit different....

The z-axis accels/decels. a lower mass, but that mass could be unbalanced. The cutting forces should be lower. General impression is that the z-axis is less demanding on a motor than the other two main axes. Even debatable whether a micro-step driver is needed for the z-axis.

Having said that, our one table runs a direct drive motor and the other runs a geared motor. I really can't say that one is better than the other. But, for a heavy router/spindle the geared version should be better. The gearing gives a bigger "detent" when the motor is switched off, and the router/spindle mass doesn't need to be compensated that accurately.

I plan to run this axis with an ungeared motor as an experiment with the heavy spindle, but I could run into problems with the gas-lift's weight compensation. I have to design a coil spring alternative in any case, because everybody won't be able to locate gas-lifts as easily.

That motor mount plate can take either geared or ungeared motors - the pinion location will stay the same.
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  #27  
Old Mon 20 November 2006, 11:19
Paul A
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Hi All

If you were not happy about beveling your Guage Plate you could aways form the Z slide with a few pieces of sheet steel and a couple of BWC rails bolted between.

Just a thought


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  #28  
Old Mon 20 November 2006, 11:35
Gerald_D
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If you want to go that route, it would be better to reverse the BWC rails so that their shoulders butt against the stiffer plate, the flat one. I would just put the rails on the edges of a thinner gauge plate, and still go for the box-section backing.
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  #29  
Old Wed 13 December 2006, 02:29
fabrica
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In drawing number 10 40 330 (SA). You have given two sets of dimensions. One set for the Inch option and the other for the metric option. What does it mean?
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  #30  
Old Wed 13 December 2006, 02:48
Gerald_D
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The inch guys sell that plate as 4"x0.25"x18" and the metric guys sell it as 100mm x 6mm x 500mm. Both those sizes will work without sawing the plate any shorter.
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