Friday, August 5, 2016

The Unkindest Cut of All

Well, that's too Shakespearean.  It's not like it was "unkindest", but it was the hardest material I've had to cut.  Something ordinary machine tools won't touch. 

In the G0704 CNC conversion I'm doing, I encountered something I wasn't comfortable doing.  A picture is worth a thousand words, so one view from the conversion DVD.
This is the Y axis ballscrew.  The flange of the ballnut is visible just above the centerline, on the ballscrew.  You can see that there's a vertical cut there, just left of the text box, cutting into the flange and cutting open one of the mounting holes.  Although not shown here, this gets attached to a mount that I machined a while back, and the whole thing sits in the base of the mill replacing the current hardware.  There's just one minor problem.  Across its widest points in this orientation, the width of that ballnut is 1.88".  The slot it moves in is 1.84".  I need to take off 50 or 60 thousandths - half on each side.

The "instructions" (as voice on included video) are to just take an angle grinder to it and take off a little.  Nothing critical.  Doesn't have to be pretty.  The only problem is I've never used one.  I need to cross that line at some point, but right now, I'd need to take that outside and do it on the porch, and that's easier said than done.  It needs to be held in something, some sort of vise, and that vise needs to be held by something.  Unlike the powder coat toaster oven, I can't just stick the vise on a shelf; it needs to be secure.  In case you're thinking this, I can't cut it on the milling machine itself, either.  The steel is so hard that a file just slides on it, not cutting at all.  Too hard to cut with a carbide cutter. 

After puzzling over this cut for a few days (instead of just building a back porch workbench), I came up with a way to use things I already have.  In particular, I have some lapidary (rock cutting and polishing) equipment that includes a coarse diamond grinder.  This seemed to have a lot of advantages: it not only would grind away the steel, but lapidary equipment is water cooled, which keeps the dust from building up in places you don't want it, and keeps the work cool.  Plus, it's a diamond abrasive, which is much harder than the cutters in angle grinders or the carbide cutting tools.  It worked like a champ.  
This is cut way deeper than it probably needs to be.  I made it look like the piece in the picture above.  Instead of being close to the 1.84 of the slot, it's more like 1.55.  Since it's based on the master version, it should work fine. 

One more little obstacle out of the way.  Not only is every piece a puzzle, pretty much every cut can be a puzzle.


8 comments:

  1. A cheap 6" belt/12" disc sander with an appropriate belt does well on this non critical stuff. Has a table to hold the part square.

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  2. Don't know if this will help, but several years back I built an "outdoor vise platform" - glued two thicknesses of 3/4 plywood together sized to match the maximum exterior width and length of my B&D Workmate top and bolted a decent 6" machinist's vise to it. C clamped to the Workmate it's a reasonably stable platform, occasionally made somewhat more solid by putting a couple 30 cal ammo cans of reloading lead (about 70 lbs each), one on the Workmate front foot rest and the other hanging from the rear crossbar with a carabiner to load the hinged outward-angled lower leg sections.

    It's come in handy for doing messy stuff in the driveway or for "in the field" type work. It's turned out handy enough that I bought a second Workmate and built another vise platform (using a cheaper vise....) for long work pieces.

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  3. Workmates are really useful. I have a specialty tool permanently attached to the removable middle board, and it is a breeze to set up the stand and clamp the board/tool in it. Then it stores away under a bench.
    I used to laugh at them because of the relatively flimsy construction, till the advantage of having a work top AT the work location penetrated my noggin.

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  4. Interesting that Workmates should come up. That was exactly what I was thinking of. I have an old bench vise that isn't very good, but would be good enough for a task like this (I think). Bolt it to a piece of 3/4" plywood and clamp it in a workmate, with some weight, like Nosmo King is talking about and I think it would be the answer.

    As for grinder vs. belt sander - I have a small belt sander that I'm kind of disappointed in (2" wide belts). This is an old Craftsman special that was OK for a couple of pieces of shelving but hasn't been useful for much. On the other hand, I bought a Horrible Freight grinder specifically for this project (there are more things coming where I need to use it). A whole $22.

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  5. You don't have a vise?!!!!! OMG. How do you get anything done? Hie thee to Harbor Freight post haste and pick up their six inch rotating model when it's on sale.Then find a used heavy truck wheel,a chunk of pipe and a piece of plate to make a stand for it.You can just tilt it over on the edge of the wheel and roll it around wherever you want.

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  6. You don't have a vise?!!!!! OMG. How do you get anything done? Hie thee to Harbor Freight post haste and pick up their six inch rotating model when it's on sale.Then find a used heavy truck wheel,a chunk of pipe and a piece of plate to make a stand for it.You can just tilt it over on the edge of the wheel and roll it around wherever you want.

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    Replies
    1. We all have our vises. Sorry, couldn't resist.

      I have several, from a 2" screwless vise for the micro mill, two different sized vises for the drill press, and a Kurt copy on the Grizzly. Four woodworking vises, mounted to my woodworking benches. And the one I mentioned in my comment at 11:49.

      What I don't have is the heavy truck wheel, pipe, plate and the rest of stand you describe. That's why all the talk of the Workmates.

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  7. The problem with angle grinders is that you won't stop at just one. You want one for a wire wheel, one for a cutoff disc, one for a grinding wheel, one for a flap disc...
    If you weld they are essential. If you don't have a portaband, you'll want to get one just for cutting thick stock.
    This is a place where I definitely wouldn't buy Harbor Freight. Get something with a decent housing and beings so it doesn't explode in your hands.

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