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  #1  
Old Fri 26 May 2006, 03:31
Gerald_D
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Grinding V-profile on rail edges

The MechMate drawings will call for a machine shop with a milling machine to form the inverted V on the top edge of lengths of standard angle iron for the x and y rails. Pretty easy and economical - if you have access to a milling machine shop. But you may want to consider a variation on the following......


Grinding in radial arm saw or table saw

Then a quick test in a table saw.....


Don't try this if there is sawdust in your table-saw!

This is not the way that I had my rails made (they were milled), but I am just throwing this in here as food for thought.........
  #2  
Old Tue 07 November 2006, 11:22
Evan Curtis
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As you?re pushing the plate through and the grinding wheel is wearing down; how do you keep the edges parallel and square? Do you have to adjust the fence? Or is the wear on the wheel so minimal as to not matter?
  #3  
Old Tue 07 November 2006, 12:03
Gerald_D
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It was a thin "cut-off" wheel only 3mm thick. Not designed for feeding material from the side. And the grit is quite coarse and fairly loosely bound in the wheel. Unfortunately our table saw construction is such that a thicker blade/wheel doesn't go past the nose of the (left-hand) threaded shaft.

With the first couple of cuts, the wheel seemed to wear a lot because the cut was quickly getting lighter. Realise that all four edges are done with one setting (the plate is flipped over and end-for-end). Therefore 2 meters of edge per setting.

For the first couple of cuts I only lifted the wheel and didn't move the fence. When it got close to final shape I re-measured the wheel diam to do a final calibration. To my surprise, there was only 3mm lost on the diameter.

The last cuts were very light and all 4 flipped passes seemed consistent. The original edge was down to 1mm wide and looked absolutely consistent side-to-side and end-to-end. The fence was only moved twice, the wheel was raised less than ten times, therefore less than 10 passes per edge. (Had to do it during lunch-break when they allow me in the workshop)

Realise that I am not trying to get a 100% perfect slide by NASA standards. It must be an economic, wear-resistant, stiff slide suitable for a short-stroke z-axis on a router. Because this slide is harder and thicker than our SB's one, and because the wheel diameters are bigger, I will be able to pre-load the eccentrics quite a lot without causing excessive wear.
  #4  
Old Tue 07 November 2006, 13:45
Evan Curtis
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As I've thought about it and reading your process I see now how it could be quite accurate (more precise than SB's) If you scribe four layout lines one on each side along each edge then grind and file to the line, it might help in ensuring accuracy. The pictures you've posted look great. It appears you left a small (about 1.5mm) flat face along each edge there by ensuring the edges remain at least as parallel as the flat stock was when purchased. I'm going to have to rebuild one of my Z axis in the near future, now I have to decide between using a linear bearing slide as on the Original Mechmate and this V-Bearing slide. I really appreciate all you've shared with us.
  #5  
Old Tue 07 November 2006, 14:06
Gerald_D
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Evan, try it on some scrap flat bar stock first. I did the draw filing only to remove the right-angle marks left by the wheel. The amount removed by the file is very tiny and I wouldn't try to file to a scribed line. I don't even think the draw filing is necessary at all if the stone is finer. My draw filing started on the SB years back, and I regard it as my personal input - much like scraping bearings and beds (don't expect everyone to know what I'm talking about here hint )
  #6  
Old Tue 07 November 2006, 16:43
John_H
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Hi all,

I dont own a SB but I'm assuming this project
is a completely seperate machine all it's own?

I've built 5 small fixed bridge desktop sized
machines, But I'd like somthing a bit larger.

I'm interested in how you're working on the flat
bar. I'd be concerned that the fine grit will
do some damage to a table saw.

What about a piece of angle iron bolted upside
down alongside a cheap grinder. That provides
a 45 angle, then an adjustable block to provide
enough tension to slide the flat bar through
in several passes.

Here's a crude sketch...Hope it make sense.

John

  #7  
Old Tue 07 November 2006, 19:49
vadeem
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I cut aluminum on the tablesaw without worry about damage all the time.

I always clean out ALL of the wood dust before starting. I also turn off my main dust collector and switch to just a plain shop-vac.
  #8  
Old Tue 07 November 2006, 20:36
John_H
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I also cut aluminum on mine. Mine is a 150.00
table saw. I imagine some of us use 5-6-7 hundred
dollar saws.

Relative to an aluminum shaving, the fine dust generated from an abrasive cut-off wheel (aluminum
or silicon oxide) WILL damage your motor bearings.
I know this from experience.

What I'm interested in is a way to create the necessary angles for bearings to ride on in an
on-demand, as needed fashion.

I believe a setup like I described may work very
well, accounting for a trial & error test or two.

I have seen some surface hardening compounds in a
can, but haven't tried any.
  #9  
Old Tue 07 November 2006, 22:49
vadeem
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Thanks for the tip before I runined my $$$ saw!
  #10  
Old Wed 08 November 2006, 00:00
Gerald_D
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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?
  #11  
Old Wed 08 November 2006, 00:17
John_H
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You wouldn't likely ruin it just doing it a few
times, but it's definitly Not Good for the motor
in the saw. This aluminum (or silicon) oxide
dust is harder than the bearings. and so small
that easily gets into places one can't see.

I'd do it on my cheap saw...it's on the way out
anyhow. But I'd hesitate on a nice expensive
shop saw.

Anyway, It'd be nice to be able to make up a section of rail, maybe several feet long, as it
was needed.

John
  #12  
Old Wed 08 November 2006, 00:20
Gerald_D
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The bearings on my grinders and table saw are identical in terms of seals - I can't see why grind dust will be a bigger issue for the table saw bearing instead of the grinder bearing. We are not talking of using the table-saw as a production 40 hour/week grinder - this is a quick light job. No worse than using a belt-sander near your table saw.

The biggest damage to the saw is caused by the burr that the grinding makes on the bottom edge of the rail. This burr scratches across the table. A bit of thin plywood under the rail will stop that.
  #13  
Old Wed 08 November 2006, 00:45
John_H
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I Absolutely Agree.

I would like to set up a small scale "production"
type of arrangement, just to see and test out how
well it'd work.

Here's what comes to mind. Imagine if this "V" track
were about as cheap as drill rod material, with
about the same tolerances. And the bearings were
well..not as expensive as they are now.

That combination would VERY useful to a lot of people. And there's really no good reason such
a combination doesn't exist. It's a big world full
of people trying to figure out what to make so they can survive, but strangely enough, nobody
makes what there's a demand for?

It can't be that hard to make a relativly straight
bar that is angled on the edges.

I'll throw away a $35.00 grinder if it fails.

What do you think of the grinder idea anyway?
I see you're the only one who's actually tried to do this.

John
  #14  
Old Wed 08 November 2006, 01:12
John_H
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I should have mentioned from the start that
I'm VERY impressed by the section you made
already. I haven't seen anyone else try this.

John
  #15  
Old Wed 08 November 2006, 01:18
Gerald_D
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John, in principle, your scheme is solid. Adjustment for progressively deeper cuts would be tricky.

Also, I would add a support edge for the back of the rail (bottom left corner in your diagram). Imagine what happens down there if you are putting 4 bevels on a flat bar.........

Little $35 grinders are often very under-powered - that isn't a problem if you have time. Taking lighter cuts will force you into a good finish. Also, the larger the stone the better - I don't know if $35 grinders can safely take bigger stones.

The experimenters must watch the legal speeds on stones, wear eye protection, maybe even gloves for that sharp burr...

For long lengths, one is going to need a long table to carry the weight - you don't want the rail to droop over a table, lifting the center section away from the wheel.
  #16  
Old Wed 08 November 2006, 01:40
John_H
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Well then a $100.00 grinder. I became Very
interested when I saw you'd actually done it.

If attention and care were put into a tool/jig intended to do only beveling edges, it may be worth the trouble. It could even be stepper driven very easily.

To try and do a "quick & dirty" on such an important part of the machine is no good.

I saw your part you'd made and that's what got
me going. I'm working on a Z-axis for my machine
as we speak and I wished I could use the "V"
bearings. PITA to get them though!

I gather you're the guy who's designing this
machine? E X C E L L E N T !

John
  #17  
Old Wed 08 November 2006, 02:43
Gerald_D
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What's stopping you from making your own V-rollers?
  #18  
Old Wed 08 November 2006, 03:17
John_H
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I tried to figure out how to make the rails
first, and whether it was worth the trouble.

But to do it Precisely was going to require
a jig and I just sorta put it off.

When I saw your section the light came back on.

I'm sorry I haven't done my homework correctly here but if I understand it your project is a
stand-alone machine all it's own?

You're offering the plans alone and the end user
does the best he can.

You don't offer any parts.

I'm pretty sure I'm right with that but I will
ask directly.

I'd like to be a useful contribitor, that's why I ask. I think this may be one of the very best idea's I've seen.

I don't know about SB, but I've been rig-matizing
machines for many years and may be useful in some way.


BTW those are impressive too!

John
  #19  
Old Wed 08 November 2006, 03:47
Gerald_D
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"If attention and care were put into a tool/jig intended to do only beveling edges, it may be worth the trouble. It could even be stepper driven very easily." Apparently, that is how ShopBot make their rails. I've heard they use belt sanders instead of stone wheels, and they drive them down the rail with steppers. I guess that they control pressure and time in contact with the abrasive rather than the exact dimensions of the finished rail. Nothing really wrong with that, the exact dimensions of the rail are not critical - they just have to be consistent (parallel).

Yup, I am not supplying parts. I would really like to see guys like you standing up and offering parts to others in your area while I take a back seat. It would be nice to get a self-supporting community going.
  #20  
Old Wed 15 November 2006, 06:53
fabrica
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My machine operator has around two days of free time starting from tomorrow. I had a chat with him yesterday and he confidently said that he may be able to do the rails with the Shaper. But it is going to be a very tedious and time consuming job.I will keep you guys posted of the developments. In the mean time your suggestions on this issue are welcome before we start on the job (to make my life less miserable).
  #21  
Old Wed 15 November 2006, 07:16
Gerald_D
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Relax fabrica, go and watch some cricket!

I believe that your "shaper" and my "milling machine" are the same type of tool (different terminology in your country?). Just let your machinist do one rail first. Can you take photos for us?

Did you see how this thread developed 2 days ago?
  #22  
Old Wed 15 November 2006, 07:31
fabrica
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In my country when our team is involved in a cricket match most of guys do not turn up for work (including me).

Definitly I will keep you guys posted with the photos on a regular basis.
  #23  
Old Fri 17 November 2006, 08:23
fabrica
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This is the sample V rail that we did with the existing shaper which ahas a stroke of 600 mm. We did this just to get some confidence. I will post a better picture tomorrow since I am still to learn the finer point of using the micro mode of my dig camera.

  #24  
Old Fri 17 November 2006, 08:28
fabrica
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To do this rail we used a shaper which has a
600 mm stroke.

  #25  
Old Fri 17 November 2006, 08:38
fabrica
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The rail came out fairly accurate and the dimensional accuracy was Ok. The hitch is the fact that we can only do 24" inches at a time. We cannot align the 24" pieces accuratly to get the final lenth. Tomorrow we will be trying out another method which will give us a continous run (around 11 feet)

We plant to fix a 1000 watt hand drill to the moving head of the shaper and mount the L iron on to the wise and move the bed horizontally to do the profile cut. The bed could move horizontally around 36" (motor Driven). Once bed comes to the end we would unlock the wise and push the L iron foward to do the next cut.

We are planning to use a end mill cutter mounted on the drill to get the 1" height cut then use a bevel cuuter to do the sides.

Your comments are most welcome.
  #26  
Old Fri 17 November 2006, 08:39
Gerald_D
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That is indeed a shaper and not a milling machine. It appears to be well-kept and your machinist must be proud of it. But, I don't believe you can make a rail longer than the 600mm stroke with this style of machine.

Oops, I posted too quickly - while you were typing.....
  #27  
Old Fri 17 November 2006, 08:52
fabrica
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WE are trying to get the bed to do the feeding and the drill mounted on the head to do the cutting by using end mill and bewell cutter. Looking foward to your comments.
  #28  
Old Fri 17 November 2006, 09:08
Gerald_D
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I am impressed with your enthusiasm and ingenuity for this project. For cutting the bevels, a 1000 Watt hand-drill should have enough power, but I am worried that you have to remove a lot of material to get to the 1" and that the hand-drill won't cope with that. Can you get very thin grind discs to cut off most of the edge of that rail?

Also, the vice will only carry a short length of rail inside its jaws, while you will be cutting a long path of 36". Most of your cut will be outside the vice and the rail will bend. Unless you put a strong/long support under the rail. I have the unfortunate feeling that you may be cutting a series of 36" long curves.
  #29  
Old Fri 17 November 2006, 09:20
fabrica
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No Gerald, I think you have got me wrong. We will be moving the bed not the Wise. The bed is holding the wise from underneath. The bed movement would be perpendicular to normal cutting head movenemt of the shaper. The wise would stick to the same position in the bed during the cutting process.

To cut the angle iron from 2.5" inches down to size (a little above 1") we would be using modified chop saw which will enable us to feed the angle iron parellel to the cutting disk of the chop saw.
  #30  
Old Fri 17 November 2006, 09:22
fabrica
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Sorry one more thing to mention. By using the chop saw we will cut the angle iron down to a size which is little above 1". The final cut would be done on the shaper with a end mill cutter.
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