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  • Jaakko Fagerlund
    replied
    Originally posted by loose nut View Post
    The wheels that LMS sells for those tool post grinders are a crap shoot at best, you WILL need to balance and true them up.
    As with any grinding wheel.

    Go for the QCTP mounted small air (pencil) grinder, there are plenty of supplies for them. At work we have two types, the smaller takes 3 mm shank stuff and the biger 6 mm. All kinds of stones in different lengths, sizes, materials and hardness are available, we get them from a mold makers tool supply company, costs pennies each.

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  • Toolguy
    replied
    I think the air grinder in the boring bar holder will do what you want to do.

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  • Guido
    replied
    Go with the air motor as shown. A Dremel with similar burr does wonders.

    If going into multi hundred production units, consider outsourcing, or CNC.

    --G

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  • loose nut
    replied
    The wheels that LMS sells for those tool post grinders are a crap shoot at best, you WILL need to balance and true them up.

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  • brian Rupnow
    replied
    Maybe for the small amount of grinding I want to do, this is what I want. My shop has an air supply. this one fits in the boring bar holder on an AXA toolpost. It sure looks a lot handier, but I suppose a great deal would depend on what type and grade of "mounted points" (grinding wheels potted onto arbors) are available. it would certainly be better than having to unbolt the compound rest and all of the nonsense involved with the first grinder I showed. It would also be angle adjustable and could be fed at an angle. Remember, this is only for needle valves and perhaps very small (as in 3/8" diameter) valves vor i.c. engines.

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  • MrFluffy
    replied
    I started off with a cheap grinder mounted on the cross slide, but I didn't get the results I wanted.
    So I made this out of it (this was what the leather belt joining q was for). The grinder drives a real grinding spindle at about 10k and mounts into my toolpost and there is a foot pendant on the floor within reach of my foot to turn it off and on easy. I'm happy with the results from it.
    I probably can only get away with a setup this outrageous because of the rigidity of the multifix B system I use...

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  • Stepside
    replied
    To polish the pivots on the Street clocks I use some 1000 and some 2000 grit abrasive lubricated with a very light oil. The first step is to cut as smooth a surface as I can. The polishing boards are the different grits of abrasive spray glued to some flat 1/8 inch Aluminum. The boards are about 1/2 to 3/4 inch wide and 6 to 8 inches long. One has to make sure you are polishing with the abrasive rubbing on the entire surface. Do not stop moving the board and use a light pressure. Light oil and a light touch and you should havea great finish. If I am being really careful I will disconnect the lead screw so the only thing moving is the headstock spindle.

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  • J Tiers
    replied
    Eh.....

    grinding is typically lower force work.... with so many cutting edges, it is easy to remove a lot of material (relatively) with little force.

    AND for something like what you describe, the last thing you want are a bunch of parallel rings around the needle..... you will need to polish it or use a finishing cutter anyway, and may as well grind. Then also you may want to hit it with a finer wheel to finish/polish the needle. Finishing cutters tend to have wider cutting areas (nose radius) and can chatter, have issues with cutting force, etc, due to a weak workpiece, even when finely honed.

    While the bearings etc are important for fine work, if you can obtain a grinder that takes a reasonably common wheel size, you can do fine. Grinder hands will cringe and declare it won't work..... but I have used many wheel types in mine.... even cutoff wheels. Those actually do pretty well for certain jobs.

    The best finish will of course be obtained by fine bearings etc..... but if you make several passes, or go slow, the effect of the grinder bearings will be averaged.... the LATHE bearings will dominate. Yes of course this will be immediately and indignantly denied with curses at my stupidity. Ignore that, try it, and see.

    Dressing the wheel is more-or-less of a necessity to get anywhere fast, since the bearings are much less of an issue than a wheel that is off-center, or out-of-round.

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  • Mcgyver
    replied
    Originally posted by brian Rupnow View Post
    I am assuming that with a toolpost grinder like the one shown in the picture and link, that I could grind these small items to the required taper.
    I'm not convinced the grinder is the answer and would also have concerns about the quality - you might just being buying more frustrations. Work will still bounce away from a grinding wheel to some degree and super cheap spindles won't give a very good finish

    There are ways to turn very small diameters. The first checks you thought of - very sharp tool (this means stoned not just ground) and having it a centre height (the smaller diam the more this matters). With sharp hss at centre height its easy to cut less than a thou off - and reducing forces is the first thing to try to be able to work on small dia stuff

    Beyond that, the two usual techniques are 1) start with a much larger diameter and take one big cut. ie if you a 1" long at 1/16 start with 1/4 or 5/16 and do it in one cut. The larger material will support things. The second way is to move a little bit out of the collet at a time and turn to diameter - sort of a manual swiss lathe approach to things. Careful work and bit of polish and you can't tell it was turned in sections. Presumably you could even do this with a three jaw if you were careful to keep the orientation.

    In picking up the already turned section, put some magic marker on whats cut and advnance until it scrapes of the market but no metal, you're there.


    Of course, this would leave me with no way to set up angles to grind tapers, so I would probably have to have an adapter plate with drilled and tapped holes at whatever angles I would most commonly wish to grind on tapered needle valves.
    I'm taking this to mean you somehow dress the wheel, then angle the TPG, pin in place and present to the work at an angle to get your taper? I see that as a big challenge. First your trying t grind the full width of the wheel which will really make the work bounce away - sort of anti solution if the problem is the work is so small and flexible. Secondly, you want the wheel moving over the work for a good finish, not just plunged in one position

    I would either turn it using suggestions above or trying rigging up a foredom or something with a small wheel. The foredom gives a reasonable good little spindle, if you have to buy its got a 1000 other uses (vs a low end tpg), it'll be small enough to mount on the compound so you can use it to cut the taper and the tiny wheels will minimize the force on the flexible work. but first i'd try turning it
    Last edited by Mcgyver; 03-12-2013, 09:37 AM.

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  • brian Rupnow
    replied
    It would be much simpler if the grinder could be held in one of the tool holders on my AXA quickchange toolpost. Does anybody know of a company that sells a set up like that?

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  • The Artful Bodger
    replied
    Brian, that little grinder will I am sure have some basic functionality so if it was me I would buy it and see what it could do. They are not very expensive in this country and I assume in yours too, probably cheaper than here.

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  • Jaakko Fagerlund
    replied
    How about drilling a small hole in the end of ascrew and loctiting a piece of ordinary needle in there?

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  • tdmidget
    replied
    Can't be much of a tool post grinder at that price. The bearings in real one will cost more than that. It has no ID spindle and no provision for speed change. The wheels Are likely crap as they give only the grit size (60 and 80) which are too fine for that kind of work.
    A tool post grinder does not a grinding machine make. The mini lathes that it intended for are POS. A ground finish won't change that.

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  • darryl
    replied
    Sounds to me like the cutter is too high. I have an 8x18, not that it matters, and I can cut a diameter down to about 20 thou before it breaks off. Sharp tooling is needed for sure.

    But tool post grinders sure can be handy. At one point I made a few axles for slot cars- these had a taper on both ends. I ground both ends to a point, then set up a kind of fork which could carry the axles between the tines. Inside out between centers. The fork was mounted on a base which fit the bed ways. The fork shaft is vertical and can be rotated so you can set up any angle. The distance between the forks is adjustable. Each tine has a divot in it, and they are set up to be at center height.

    I used the TP grinder mounted to the cross slide to grind the tapers, and turned the axle shaft by means of a string and bow- basically just 'sawing' it back and forth. Bit of lube in the divots and it went pretty easily. I just moved the carriage back and forth while grinding until it sparked out. This was music wire, and there's no way I would have gotten that nice a result by turning.
    Last edited by darryl; 03-12-2013, 02:52 AM.

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  • Gary Paine
    replied
    Originally posted by brian Rupnow View Post
    I simply don't have the ability to turn small precision parts like needle valves for miniature carburetors on my 10" x 18" lathe. Once I get below about 3/32" diameter stock, the material just flexes away from even my sharpest HSS tooling.
    Brian, I'll leave the grinder question to those more apt, but I wonder if there's not something you could do to fix the above mentioned problems. With my jeweler's lathe, I can chuck a piece of 3/32 and reduce it to nearly nothing without bending or breaking it. And that is with either the cross slide or a hand rest and graver. Is your problem maybe going way too slow for such a small diameter, cutting too deep for the work, cutter not right on center, or cutting angles wrong? Are you maybe trying to use a carbide tool on that small part? I'll bet their is something obvious causing the problems.

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