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turning bushings on the grinder.....advice needed

greg y

Plastic
Joined
Mar 24, 2012
Location
otis orchards, wa
Greetings ya'll, new poster long time lurker here.

I have recently aquired a 6x12 surface grinder and I need to build some bushings that will be .500" id and vary in steps of 2 tenths per from .702-.706". I plan on using drill rod and boring the id on my lathe and rough turning the od. I have a small set of centers that I could modify into a fixture with some advice, or would a spin index be the answer? The bushings will be about 1.5" long.....and I can vary that by about .25" if need be.

Looking at the spin indexers I am unsure if the little grinder has the travel on the cross to allow it to fit. I would appreciate any advice or pics on how to attack this. Production speed is of no concern, these are for myself in my own shop. I will include a pic of the centers I purchased from a local retiring machinist. If anyone knows their original application......please share.

Lastly, I am green as spring grass to surface grinding aside from some automotive stuff. My machine uses 7x1/4" wheels, I know that much....I am not perfectly clear on wheel hardness and compositions. I understand grit, but appreciate advice on what wheels to stock up on.

Thanks for any help.
Greg.
 
Here is the small set of centers I have. They are made by Sheffield. One side can rotate, the other has a screw to drive it like a tailstock.

IMAG0238.jpg


IMAG0239.jpg
 
I would get a good spinning fixture (not the $249. version) that spins in bearings. What you have is some kind of center for inspection, no means to rotate the part no way to secure it on your chuck, and probably too flimsy anyway. Leave your pars an extra inch long to grab onto in the spinning fixture and grind away. Keeping the thin wall part cool will be a challenge without coolant. You will need something like this for these kind of tolerances. Spin/Index Grinding Fixture - Cylindrical Grinding Fixtures & Accessories | MSCDirect.com
 
I agree with what RJT stated. What you would need would be a "whirlygig" made by Harig, Suburban, ect. They're pricey, even used, but worth every penny IMO...

Harig Uni-dex 5C Collet Indexing Fixture, Center Height 3.00", 360 Graduation | eBay

No aff. with the seller. If you reamed or bored the ID, then it would be a simple matter of making a shouldered stub arbor (mandrel) with a screw hole in the end to hold the bushings while grinding. Just cinch them on with a washer and screw. Once the arbor is indicated in the whirlygig, they should repeat very well. Going in .0002" increments, heat will be a killer. I'd set up some type of cold gun on the bushings to keep temperature in check. The wheel you would use will be dictated by if these bushings are hardened or left soft. If hardened, I'd suggest a Norton 5SG 46H or 46I. This wheel can be used on them if left soft also, but in that case a 46J or 46K could also be used. A 60 grit wheel could be substituted for the 46 grit for a slightly finer finish (especially if left soft), but this would add to the heat issue. I'd stay to the 46 grit.

P.S. I'd recommend making these bushing in order of largest OD to smallest. That way, if you do get a couple of them warm & they shrink back, you may have covered another size you were going to grind anyway. :)
 
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Thanks. I guess I will camp out on eBay for a while. I can buy 36 bushings for the cost of the wirlygig.....but then I wouldn't have the tools.
 
If you want to hold 2 tenths as well as maintain concentricity, it would be best to do the part ID & OD on a "good" spindex without removing it between operations.

If you do not intend to harden the part, I would argue that it would be best and easiest to make them complete on the lathe. You can easily make a CI or aluminum OD lap to finish the OD's if you are leery of turning and (freehand) polishing. I would also argue that your .0002 tolerances won't last long in the unhardened state.

If you intend to harden them, then it will be necessary to leave some stock and finish the ID on the grinder with a highspeed head/attachment.

High speed attachment for T & C grinder, they are also made (& sold on ebay from time to time) for SG's

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If hardenend, I start the cut-off land in the lathe, and leave a very thin fin connecting to the intended part, from the section to be gripped in the spindex. This minimizes distortion and make is easy to finish part; eventually severing it with a thin cut-off wheel.

Turned, hardened bearing race blank; nearly parted off before hardening.

smt_SCM_bb3.jpg


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New replacement inner race after finish grinding
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It is possible to finish the parts on an arbor between centers, especially if you make a pulley to drive it. The pulley can be wood or plastic, as long as it is round & concentric so as not to induce lobing by variable drive rate. Your centers are light, but they could work. I made the expansion arbor shown, but have a set of factory made ones, too. They would still need to be qualified depending on your requiements for concentricity. One of you most difficult tasks will be aligning them across the grinder magnet so they do not create a taper.

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Just some ideas. This work is easier to do on a Tool & cutter grinder; but can be done on a surface grinder. Your centers could be adapted. A good spindex would make it easier on the SG. It would still be worthwhile to analyze whether OD grinding soft bushings has enough extra merit over finishing on the lathe to be worthwhile. If the bushings are to be hardened, you will also need a high speed head for internal finishing; though a "good" die grinder could be contrived to fit the SG grinder head with a bit of bracketry.

My personal suggestion would also be that if you have never done any of this work before and if you do not currently plan to harden the parts; the best course to start would be to get a cheap import spindex and try it to see if you want to go further. One advantage of the spindex is that since the spindle slides, the part can only be co-linear within small limits (parallel sides/cylindrical). Any other method requires careful set up and indexing to establish that parameter. I have a nice Suburban Grind-Mate, but use the cheap spindex more often.
smt
 
I have made a couple on the lathe. The surface finish is acceptable, but I was hoping to take advantage of the grinder that now sits in my shop. For me, holding 2 tenths on the lathe is no easy task and I had envisioned turning the bushings to about .0005 shy of my number and finishing on the grinder. If it is going to cost me $1500 to tool up, I will spin and lap them.....or see if I can cobble up a fixture from my pile of goodies.
 
Deals do come up occasionally on whirlygigs, but they are a bit rare. I believe a forum member here had one for sale a few months back for ~$350 (I didn't go back through to check, though). For your application, you could turn them as you mentioned or even set up a makeshift toolpost grinder for your lathe. Concentricity would almost be a non-issue, then. If you do harden them, they'll probably egg the I.D. pretty good, as SMT mentioned.

I sure wish our shop had a T&C grinder as Stephen has. Versatility is their playground...
 
You've got nothing to lose by trying your current set up & centers. As mentioned (& shown in photos), I would use an arbor between the centers to hold the bushings you described. There will be too much friction, as well as marginal accuracy, if you try to merely count on a chamfer in the part with the 1/2" bore to locate it between centers without. I think you can pick up single arbors with expansion sleeves in that size for somehwere in the $20 -$30 range though i have not checked recently. Or make/grind a solid bar with a shoulder and feature to locate/drive the bushings.

As also mentioned, a cheap import spindex might do all you need, has the advantage of forcing the OD to be cylindrical due to the slide travel; and is inexpensive to experiment with to see if you want to go further. Even if you decide to get something better, the spindex could well be your prefered method for quickly spinning down shanks on hardened tools, making hex, square or other punches, etc, etc. I use the cheap one more than my Suburban.

smt
 








 
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