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  1. #1
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    Default Need slitting / slotting advice

    I need to make some reducer bushings for a Gorton pantograph. The pantograph has a 5/16 collet, and I need reducers to 1/8 and 3/16.

    Im starting with drill bushings, already hardened, 3/4 length under the head. So all I will have to do is slot them. One slot all the way across from each end, to within maybe 3/16 of the opposite ends. Plan to hold them in a rod bored to 5/16, which would then be held in a collet fixture. I dont have coolant on my surface grinder, so grinding will be dry.

    Ive got 7 x .035 wheels, reinforced and non-reinforced. Which should I use? For a shallow slot Id be comfortable with the non-reinforced, but as Ill be going almost 3/4 deep would the reinforced wheel be a better choice? Both wheels are 60 grit. Will they leave comparable burrs? I can stone off outside burrs, but any on the inside will be more difficult.

    Id prefer to have narrower slots, especially on the 1/8 bushing. I see that .015 and .020 rubber-bonded wheels are available. Would these be a problem?

    Plunge in one pass, or feed longitudinally with small depth increments?

    Id much prefer to do these with a slitting saw, but like the idea of starting with pieces that are already to size and will require no hardening.

    Would appreciate any advice.

  2. #2
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    Any advice? I’d rather not start by snagging parts and blowing up wheels....

  3. #3
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    My guess you may be doing this in a surface grinder. Be sure the hold device does not crush the part to tighten on the wheel sides.
    (Actually, I think lathe turned and saw cut bushing made of CRS would be fine).
    Are you intending to stand part vertical or hold horizontal?
    Surface grinder down feed has the most control so you might try a vertical hold of the part and with slow down feed make wheel act like a cut-off wheel. Hand bumping the wheel od with a carbide brazed tool bit to restore the good flat bottom, width, and corners every once and a while. Yes, with holding the dress stick at angle so it does not catch wheel.
    This vertical hold with positioning the part just down wheel or left of wheel center line, so no catching or climbing.
    Problem is part vibration as a bump stop to the left side might tent to crush part into wheel thickness if close to the grind. A bump stop away down part is another possibility.

    Perhaps best:
    Holding the part horizontal perhaps with the bushing head to the right one might set the long travel stop for end of slot with stop set at table travel going to the left to bump the table stop. Set a flat bar under the part so not able to flex down. And an end stop bump to the left of the part. Use a slow down feed .002 or what on the stop and then travel part to the right for grinding…with no down feed when out of the part (for travel back to stop) so to insure no climb grinding (but don't go too fast to hard bump the stop) . The carbide hand bump used to flat OD dress the wheel. End block-in set to the left end of the part. Problem there is when wheel begins to cut bushing head and so more work for the wheel. Perhaps the bushing head should be reduced diameter before grinding slots. Yes it is common to drop a shim (s) at end stop to insure not to bump the increased stock at the end where wheel may make full contact. perhaps .015/.020 every once n a while.

    Hand bottle coolant spray might be good to insure part does not swell into wheel sides as stresses released may tend to spring part.

    Yes down feed and travel feed ..try to keep spindle speed sounding normal fast..slow/slowing sound means problems. wheel rounding will slow down speed and have more potential to bind in grind..a bad thing.

    Holding the part for second end a problem because you can't (should not) crush the part with using a block-ins on both sides of part. I might use only one side, side block-in with part setting on the chuck. Having a opposite side end stop.and a near touching .001 or so at the far right rear of the part. Yes the head would require holding off the chuck
    so likely set it on a v block with a hold down wedge for both ends..
    Last edited by michiganbuck; 03-25-2019 at 03:02 PM.

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    Many thanks, Buck, for the advice.

    Any thoughts as to whether I should be using the reinforced or the non-reinforced wheel? I’m thinking the non-reinforced with it’s smooth sides would be less apt to grab. But I’ve never used one that thin (Norton, .035”) and don’t know how delicate they are. Are the even thinner (.015” or .020”) rubber-bonded wheels suitable?

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    Big problem is tightening such a wheel on the mount..Good to think about that before you even try. Holding onto the wheel while tightening is difficult with not cracking the wheel. Better that you hold the mount not thre wheel.

    They can bend sideways in use ..but seem the slightest side push when they are not running will break them. Yes use blotters. Such wheels are very tough in use if you don't cross feed into them..And don't let the job slow wheel speed/RPM..

    Grind side they are tough but on climb side they are not tough at all.
    Non-reinforced wheels grind much better and act like a grinding wheel. Putting them on the mount nice and straight takes caution..

    I like to come in on the grind side to a slug to grind/dress the OD true.
    Yes the grind side is the table going to the right into the wheel..and sparks going to left...on most grinders.

    Good to have good running mounts so they don't side wobble.

    Set up is important as you don't want the part to move or come up.

    Just handling them loose and taking them out of the box needs care.

    Back in the day we would Whack/ whack hard and rough across solid carbide with such parting wheels.Carbide setting an a paper card so not to harm the chuck..Carbide blocked in loose so it could bounce and wobble a bit..The carbide would start to change color and crack straight across. Yes back when diamond wheels were expensive..Now a days cutting carbide is better done with 1/32 - 1/16 or so diamond wheel with using down feed and the carbide left hanging off so it can just fall off.

    OT : Cumberland Maine looks like a very nice place..

  7. #6
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    Follow up: finally got around to running these, and it worked perfectly.

    Used the Norton 60 grit non-reinforced wheel. Workpieces were held in a drilled and reamed holder, held in a 5C collet fixture, vertically. Holder was slit with 1/8” slot on mill, set screw from side to hold workpiece at bottom end (below where slot ended) for first pass, slotting from head end. For second slot, workpiece (drill bushings) inserted into holder with head in a long counterbore, with large screw in counterbore to hold bushing head against the counterbore ledge - so no compression of slots.

    After I got through the bushing head, ran with downfeed of about .050” per pass. I had not bothered dressing the wheel edge square and was worried it might pull to the front or back, but saw no drifting.

    I used my standard bushings on the arbor, which are about 3” diameter. Had thought about making larger arbor bushings to eliminate any wheel flutter, but was not a problem.

    Buck, you are right about those wheels being delicate. May have heard a crack when I removed it, but not certain. Probably should drill some holes in the wheel adapter to hold it with a pin or spanner, rather than trying to hold the wheel.

    Thanks, Buck, for your good advice.

    Cumberland is indeed a nice place - now that the last of the dirty snow has gone, the mud has dried up, and even the black flies seem to be ending. Saw a coyote chase a deer across the road yesterday, which was about as much excitement as we get here.

    John

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