Bridgeport Spindle Woes

The spindle in my 1J appears to have what I think is axial runout. Using a precise drill blank and quality collet, I get about 0.002" runout near the collet, increasing to about 0.005" when I measure 3 inches further down. I used 2 different drill blanks and 2 different collets and averaged the results.

I hoped there might be a burr or maybe that the guide pin was sticking out too far. The guide pin possibility looked even better when I saw that the high spot was aligned with the pin. I thought maybe the pin kicked the collet out when it was tightened and tilted the bottom towards the high spot.

Unfortunately, none of the easy problems panned out. So what is the most likely cause? Bearing misalignment? Screwed up socket in the spindle? Bent spindle? I think it has been this way since I got it about 6 months ago - I just didn't realize it until I tried to do some precise drilling.

I'm assuming that if I have the head rebuilt, this is something that would be fixed during the rebuild? Can anybody recommend a good rebuilder near central Ohio? There is a rebuilt head on eBay, but it's in Florida. Shipping would kill me.

I would greatly appreciate any ideas or suggestions. I suppose I've learned a bit if nothing else...

Thanks, Wallace

Reply to
Wally Blackburn
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id pull the collet out, & indicate the id of the spindle. also check for bearing slop

Reply to
Wwj2110

Thanks. Someone else suggested the same. My test indicator is a

0.001 grad piece, while my dial indicator is 0.0001, so I tend to use the dial indicator when I can.

I checked the inside and it is the bore. I got crazy last night and dressed it with a boring bar clamped in the vise. I actually cleaned it up quite a bit. From 0.002 near the collet to 0.0005; from 0.007 at 3" away to 0.0018.

I have an indexable boring bar that is too big for my 10" SB (part of an auction lot). I think I'll order a new insert for it and shorten it for rigidity, and try and get it a little better.

Thanks, Wallace

Reply to
Wally Blackburn

The taper is what I would be suspicious of. I would also pull the drawbar & make sure its not bent.

Reply to
Wwj2110

No, now that you've got it mostly true, put a fine grinding wheel on a Dremel or similar tool, and mount that in the vise. I assume you have already tilted the head to match the side of the spindle taper to the knee travel (or another axis). Run the grinding wheel in and out of the bore, and check the taper with blue dye and a known-good end mill holder or other precision ground arbor to make sure the taper you are grinding in is correct. You want the spindle rotating slowly opposite to the grinding wheel.

I have made R-8 taper sockets this way for gauging applications, and they turned out very well. (Actually, I used a real toolpost grinder on the lathe, and set the compound for the right angle.)

Jon

Reply to
Jon Elson

Jon..your just the man I want to ask about a few things...

Ive been asked to regrind the spindle noses on a bunch of Hardinge lathes..5C taper.

I want to make a fixture that will clamp on the dovetail (ways) and allow me to go in and dress out the taper. Ive seen as much as .003 run out on a worn spindle nose.

Do you have any suggestions on what grinder to use, and stones, and any suggestions for fixturing?

Most of the lathes that need doing at the moment, are chuckers, and they have no compound, so I need to be able to set the grinder to the proper angle, then move it in and out at the 10' angle, and also to move it in Z once Ive clamped the fixture to the ways.

I figure if I can make a decent fixturing setup, adjustable for both wide and narrow dovetails and of course, center height, it would be an additional $ervice I could offer my customer$.

Any suggestions would be appreciated

Gunner

No 220-pound thug can threaten the well-being or dignity of a 110-pound woman who has two pounds of iron to even things out. Is that evil? Is that wrong? People who object to weapons aren't abolishing violence, they're begging for the rule of brute force, when the biggest, strongest animals among men were always automatically "right". Guns end that, and social democracy is a hollow farce without an armed populace to make it work. - L. Neil Smith

Reply to
Gunner

Well, I used a TheMac toolpost grinder. If you can get your hands on a TheMac or Dumore TP Grinder, that is clearly the way to go. Even if the TPG is not in the best shape, it will run a lot true-er than a crummy Dremel or air die grinder.

Having done something like this when rebuilding my Sheldon, I would recommend borrowing the compound slide off a medium-size lathe, 11-15" swing. Make a fixture to adapt the compound to whatever is available on these lathes. If you can't borrow a compound, then you can probably buy a used compound slide from one of the brokers.

You will want to use the internal grinding arbor, and mount a 3/4" or so wheel. A pretty soft wheel is good, but if you are going to take off .003" runout overall (not just some dings that throw the taper off that much) It will take several passes, and then redress the wheel before the finish pass. You run the spindle opposite to the grinding wheel at a slow speed. Once you have the angle set right, the actual grinding pass takes only a few minutes.

I gauge the angle of the taper with a known-good solid arbor that can be blued and rotated in the spindle. When the dye transfers evenly along the length of the taper, the angle is right.

Jon

Reply to
Jon Elson

If I were doing this (and I will be, someday, the small cataract lathe in my shop has the plain bearing spindle buggered, so it'll need re-truing) I would use a hardinge DSC compound, like the kind they run on DV-59s. Real solid and the angle is adjustable.

I don't think that slide fits the HC like gunner is doing, because - and here gunner will correct me if I'm in error - the HC uses the wide dovetail bed, and the DSC is for DV59s that use the narrow dovetail. But I betcha a coke that this particular slide could be modified to fit an HC without doing more than moving the clamping assembly further out by an inch or two.

Jim

================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ==================================================

Reply to
jim rozen

Correct, dovetail width is different..however..so is Center Height. Because of the differences in top of way to center of spindle..Im going to have to build in a height adjustment. Probably something simple as a riser block that comes out when doing DVs

Gunner

No 220-pound thug can threaten the well-being or dignity of a 110-pound woman who has two pounds of iron to even things out. Is that evil? Is that wrong? People who object to weapons aren't abolishing violence, they're begging for the rule of brute force, when the biggest, strongest animals among men were always automatically "right". Guns end that, and social democracy is a hollow farce without an armed populace to make it work. - L. Neil Smith

Reply to
Gunner

I suspect the toolpost grinder that you would use would more than make up the difference. Maybe put the rise in the mount for the grinder?

Jim

================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ==================================================

Reply to
jim rozen

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