Grinding the chuck on a model B Thompson

jljim · May 27, 2016

My recently aquired model B Thompson has a 12x40 chuck. From the center of the chuck to either end it drops about .005 with an indicator on the wheel head. It also drops another .005 from the back to the front edge making a total error to the front outside edges of nearly .010". This error was mirrored in the first test grind using about 10x30 area of the chuck. The indicator test was run with the table way lube supply shut off while slowly traversing the table and the wheel head. I'm thinking I should probably lift the chuck and clean the mounting surfaces before grinding or should I just grind ?

michiganbuck · May 27, 2016

Think you have too many factors in checking off the wheel head. Could be the chuck top or the bed ways.
Would find a straight edge 40” (perhaps plate check something if not having a real straight edge)

oil the ways by hand before running it much.

First you see if the chuck is really flat with day light under st edge or a shim feel for a rough idea (+- .003 or so) by setting st edge on the chuck with mag off.
Next set the straight edge on chuck (still mag off) and shim it up to zero - zero for perhaps 30’.. Then running the indicator (long travel) along the straight 40” you see the condition of the bed ways.

At center with indicator on st edge turn mag on and see if anything changes.

No sense grinding the chuck if it is going to be belly or concave when done.
Front to back (cross)could be wheel head slide. They needed correcting once in a coon's age.

it is a great machine worth the two weeks of scraping if it needs that.

QT: [From the center of the chuck to either end it drops about .005 ] doesn't seem like normal wear to a chuck.

Word to SG buyers... Good to check chuck for being flat from its last grinding, That tell a lot. Check the edge away from the bump rail long way.

jljim · May 27, 2016

Tested the top of the chuck with a 48" Brown & Sharpe camel back that has been recently qualified. The chuck top is definitely high in the middle, .005 under each end. Front to back check with 12" Starrett straight edge looks flat, .001 feeler gage won't go under anywhere I checked.

michiganbuck · May 27, 2016

If you hand feel (spindle not running) the chuck center with the wheel and note the down hand wheel number. Then go (long) to chuck outer edges and note the same number then grinding the chuck will still be out of flat and just the same.

Note zero at center and -.005 (more down feed)at outs then grinding chuck will make chuck flat with hitting and grinding the center area first.

Some used Thompsons with end covers off for space saving. some shops used air hoses to blow off grit, some shops ground over-weight and tall work, some machines lost oil for a time all leading to a machine going out of flat.

One big used G&l bought by the Star factory had two heavy chucks and would grind the out ends -.005 or so.. it needed re scraping so the seller hired a scraper hand to come and fix it. Likely the weight of the chucks mounted that way and perhaps the weight of the work was too much for the bed length, Perhaps years of running full length.

If you find it good to grind.. I would pull the chuck, fine side hone with oil and check for near dead flat the pad and bottom of chuck, put chuck back with indicating the front edge for square, set back on oiled or thin grease surface and bolt down with a good one hand pull to normal or short length wrench. Yes you grind the back over lip rail to make square.

I know some like to grind the chuck bottom but I don't. Except when a machine is re scrapped and the the chuck needs a lot to come off.

jljim · May 27, 2016

The center and end touch numbers confirmed the straight edge results, high in the center. The front to back error is still an issue. I lifted the table shortly after setting the machine in place and the ways looked pretty good. I'm going to lift the chuck this weekend and deal with what ever I find there. I'll survey the chuck surface again after carefully bolting it back down. I did my much smaller, and older, 6x18 Thompson a couple years ago. Only needed a couple thou to clean up and its been fine ever since.

michiganbuck · May 28, 2016

With the touch test confirming high center in the chuck (so not in the machine) you might see if the chuck bottom is the same error so will need to have the bottom dead flat also. You can scrape it or grind it.. to .0002 or so. but before finishing the bottom ...You may have to filp-flop the chuck to be sure it is not full of stress. Check the bottom and note error, then grind .002 off top, then check the bottom again to see if it changed from relieving top side stresses.

I treat grinding a chuck like transporting an A bomb.. One can't be too careful because a burn can put stresses in it that take years or never come out. I grind wet, feel the chuck often, over travel the ends or pause (for a one to three count) takes perhaps 15 minuets more and I never get it hot (I don't even like warm).

For the cross you might shim up a good 12" parallel (or the like) to zero and then run the wheel head across it it see what you can expect there. need to know if that .005 is the chuck error or the wheel head slide even before you grind the chuck..

You could shim up the 48" Brown & Sharpe camel back facing up then run an indicator down to see what she is capable of running long.

Richard King · May 28, 2016

Many of those machines had bronze spindle bearings and when they get worn and loose they will grind the ends of the chuck low. remove the wheel and put a mag base on the wheel guard and indicator on the straight spot behind the threads and before the taper and make up a lever with a 2 x 4 and put about 25 pounds pressure on the underside of the threads and see how much clearance there is. Do the test with the spindle cold and warmed up 30 minutes.

Also put a Kurt type vise on the table or chuck and then put your B&S straight edge in it and zero the middle 24" by tapping the SE with a soft blow hammer. Should be able to indicate it (+.-) .0001 and then move the table out to the ends of travel and see what you get. On the in and out,have you adjusted the gibs on the column and saddle?

I am assuming you leveled the base? If you have put a level on the chuck and zero it. If needed shim one end until it reads zero and slowly feed the table and see if the bubble moves.

Let me now what you get and then wecan think of what the issue is.

If there are oil drip cups on the side of the spindle then it definitely is a tapered bushing. and I would bet that's the issue. .005"is a lot. Rich

jljim · May 28, 2016

This machine has a drip cup and 3 adjusting screws for the front spindle bearing. I have the chuck up and ready to pick with the forklift. From the looks of the rusty mess underneath, I doubt it's every been off since '54 when it was built. I will pull the wheel and check the play in the bearing. When I get the table cleaned off, I'll try the long travel test with the SE and vise. Any guess what the 12x40 chuck might weigh ? I'm thinking 5-600 lb. The machine had been in storage for several years. I loosened the all the gibs and poured some way oil in between the vertical ways before moving anything. The wheel head gib was loosened and oiled until they dripped with the Bijur pump. Pretty sure the gibs are all pretty close, will check them all again.

jljim · May 28, 2016

This is what the top of the table looks like, the bottom of the chuck is pretty much the same. I scraped a path across the ways and ran the wheel head out with an indicator attached, it held +/- .0015 across 9" of travel. I think the error was mostly due to the slight amount of rust still left on the iron since it was fairly random on the dial. If my arm holds out, I should have most of the table way cleaned off tonight. Soaking with some Blaster seems to soften the rust a little. Cleaning the coolant tank was bad enough.....

michiganbuck · May 28, 2016

looks bad but not a big deal.. Handles and what I see of the front looks nice .. Vertical import and what is under the rusty table..Have run a few Thompsons and think they are a very good machine.

tdmidget · May 28, 2016

The rust is very likely the whole problem. When iron rusts it gains in both weight and volume. It could easily have raised the center.005" or more. Clean the table, grind it flat (you don't need 100% cleanup, 50% will be fine) put a coat of a thick water resistant grease (like aluminum complex) under it and remount the chuck. You may find improvement at that point. dress the chuck and see if you have improvement. The balance may well be in the spindle bearing adjustment, as Richard suggests.

Richard King · May 29, 2016

After you clean all the rust. Be sure to have a open coarse wheel..(It been so long I can't recall wheel grades) fasten a dresseron the table if it doesn't have a internal dreser. then dress it rough and open. Like td sugests clean up grind top of table. Be sure to use coolant and lots of it. I would bet the bottom of the chuck is terrible too, so after you clean the rust off the bottom flip over the chuck and slide in .005" shim stock under the top that is now facing down on both ends and then put some .003 closer to the middle and then turn on the chuck. kiss the bottom to clean up, again with a lot of coolant and open dress.You may have to dress the wheel a few times on table top and bottom of chuck by rigging up a dresser block some now. Be sure this is attached good so nothing happens and you don't get hurt. Coolant is very important, so be sure to use it and keep everything cool. Then flip over,clean everything and grease top of table or years ago we used white lead. attach chuck. I had an old timer tell me years ago to tighten the left chuck hold down tight and put a lock washer on the right hold down and just snug it up (on electro-magnetic) so as the chuck got warm it would expand and move and not warp the chuck. Rich

michiganbuck · May 29, 2016

All great advice from Richard as usual.. only one thing I wold add, any time you feel a job is getting warm extend you over travel a bit or give a cool down count at being off at the ends.

Oh, and to have a good way to come back to the work after dress so not coming back hard.. lot of different methods, so choose the one you like..Guess the simplest is to note your dial number and how much you dress.

I know you know these things so this mostly for the new guys who might be following the thread.

jljim · May 29, 2016

Had to finish scraping the rust this morning, looking lots better now. Yes, the bottom of the chuck is just as bad and will most likely need ground. I'll post a pic when I get it flipped over. Ran the indicator over the table after lightly stoneing the ways. Front to back is +/- .001 hand feeding the head at both ends of the table and 2 spots splitting the center. Covered about 9" again, I can't reach the full travel to the rear with the setup on the wheel guard. Long travel was was also +/- .001 until the last 8-10" of table travel to the left. There was a steady rise to a max of .015 with the table at the far left travel. The same result on all three of the front ways, can't reach the rear with the current setup. Sliding the SE to the left end of the table is good, won't take a .0015 feeler. Sliding the 199 starrett along the way shows good from the left end for about 30", then the bubble starts to drift the closer you get to the right end of the table. The T nuts for the chuck are very solid (rusted) in the table. May have to cut them out to grind the table. All the advice is very much appreciated, seems the more I think I know, the more I find I don't know....... Jim

michiganbuck · May 29, 2016

Font to back .001 is not a big deal at all as it could be the wheel head slide and not the table or both table and slide..or in the column. Depending on how far you intend to rebuild *grinding the top of the chuck will take that .001 out.. it should be straight within a tenth or so (less) with the slide tight and true. Table looks good in the photo and does not have to be perfect.
Think get her lubed correctly ,tighten her up and if good scrape the top.. but yes the top doesn't matter that much except to be flat under the chuck and the chuck flat on bottom.... and top.

You might oil-hone the bottom top and bottom to see what you have now minus the rust. The bottom may be good or just need a little tweaking.

jljim · May 29, 2016

The ugly bottom of the chuck cleaned up a little easier than the table did ! Quick check with the SE across the long way was pretty flat, no big hump in the middle. Diagonal check looked good too. Made a serious attempt to remove the T slot nuts and got them all out intact to use again. Had to use my 3# Ford wrench to loosen them up

. The wheel that's mounted is a Norton
32A46-G12VBED, very porous open bond. Have 45 gals of fresh synthetic coolant and a 3/4hp coolant pump ready to go, should have plenty of volume. Pretty well talked myself in grinding the table, more pics later.

Richard King · May 30, 2016

You said "There was a steady rise to a max of .015 with the table at the far left travel"
Your saying .015" (15 thousands) ? That sounds terrible and if the table top is flat with the straight-edge I would guess the ways under the table are worn. You say " The same result on all three of the front ways", You mean the top of the table sections between the T-Slots ?

You should make another test to see if the ways are worn. I would run the table to the far right and mount a mag base on the base far right and put a .001" or .0005" indicator on the table far right side of table. Then push the table in or back toward the wall behind the machine and pull the table back toward you. You may have to use a curved pry bar if your not a big guy like me. There should not be any slop. Then move the table to the left about 12" and check it again moving mag base but resting the indicator o the same spot on the table. Youwill have to re-zero it. Your comparing the slop every 12" as far as you can move it to the left. Many times I check wear this way. If you get slop then you will need to re-scrape the bed and match fit the table. The check shows if the V ways are the same width. It's late. Good night. Rich

michiganbuck · May 30, 2016

Don't think I would grind anything until she proved flat with checking on the set-up to flat straight edge and the set-up parallel going cross.

cash · May 30, 2016

There has been a bunch of good info posted here and I will not repeat any of what has said.

One thing I have not seen commented about is have you leveled the machine? I searched the model B and it appears there was a couple differed configurations of where the levelers were placed.

Is there any chance you got a manual with the machine? On a machine this size I think you could just level off the table. But of course all has to be cleaned first.

Some of the tests Richard mentions would be my next step. You have not shown any pics of the ways? what condition are they?

BTW-nice buy on going with a machine like this.

michiganbuck · May 30, 2016

Have seen and used Colonial broach grinders and Thompsons that were so flat scraped one could move a hundreds of pounds or more table like pushing a boat on water.

Grinding the chuck on a model B Thompson

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