Wobbling carriage

[cdhknives]

So I'm trying to learn to use my grandfathers QC-54 by taking blocks of wood from angular to rounds. Fun stuff...messy, but fun. I figure wood is more forgiving and I know it is a heckuva lot cheaper!

First issue. When using the power cross feed (set to 36 TPI) to take care of travelling the carriage to make cuts, I noticed it was giving a really distinct spiral ridge. I checked the bit, no chips. Finally I noticed that the carriage was sort of snaking its way down the bed. It had a distinct wobble on the right side, maybe 1/16" at the tailstock (right) end back and forth along the bed. Firm pressure from my thumb on the right side of the carriage as it was cutting eliminated the wobble and smoothed the cut right away.

I was cutting left to right...I'd rather crash the bit into the tailstock than the chuck. Maybe I'm wrong there?

When cutting right to left, it didn't seem to happen.

I would assume it should cut smoothly both directions. Correct or not?

How do I tighten the carriage to bed travel on this lathe?

 

[wa5cab]

Unkn,

First, a bit of terminology. The cross feed, operated manually by turning the larger, single handle crank located in the center front of the carriage, moves the carriage slide (and compound if mounted) toward the front or back of the bed (toward or away from the operator). Power cross feed is engaged on the 10" and all but the final version of the 12" by pulling out the knob just below the cross feed crank. The carriage is traversed left or right along the bed by either turning the handwheel at the lower left of the apron (proper name for the front part of the carriage) or by engaging the half nuts (AKA split nuts) with the rotating lead screw by pushing down on the lever at the right end of the apron. So what you use for turning under power is the carriage drive, not the power cross feed.

Second, for several reasons, you should normally do all turning toward the headstock. The only reason for doing turning (or facing) toward the tailstock would be if turning a reduced diameter in the middle of the part in order to cut up to the right shoulder..

The carriage has two bearing plates mounted to its bottom that stick out under the front and rear edges of the ways (the two flat surfaces that the carriage rests on). These are each attached to the bottom of the carriage with two screws. As shipped, there was a shim pack between the plates and the carriage. The parts manuals show only two shims front and two rear (one each 0.002" and 0.003") but I don't actually know what would typically be in there from the factory as I have never disassembled that part of my machine and no one else here has ever said. However, I would doubt that there would be anywhere near 0.060" of shims. If the carriage can be lifted a sixteenth of an inch, there must be considerable wear on the ways and/or the bearing plates or the bearing plate mounting screws must be loose or missing. With a micrometer or a dial or vernier caliper, measure the way thichnesses up right at the headstock and at the extreme right end of the bed. On your machine, the nominal way thickness is 3/8" (0.375"). You should get 0.375" +/- a few thou. On my 3996 (1/2" ways) I get 0.495" both places. Then measure the way thickness about 6" to 12" to the right of the headstock where most wear will occur. I really have no rule of thumb for what constitutes excessive wear but will guess at 0.003" to 0.005". However, this wouldn't account for 0.060" of vertical carriage movement. The vertical movement of my carriage can't be felt. The only way I can tell that there is some is that a little oil squeezes out when I let it down.

I don't know how you have your cutter mounted of where. But to exert torque on the carriage enough to lift the right end of the carriage, you must have it hung well out to the left and maybe have the compound run well forward. Best practice is to keep the compound back to where the compound slide top surface is almost visible and the cutter tip never outboard of the ends of the carriage legs. Turning exerts a downward force on the cutter plus a side load. With the cutter tip well out to the left, the side load might be capable of lifting the right edge of the carriage. Beyond that, I can't guess without more data. All that I can suggest now is to remove the threading dial and with a good light confirm that the bearing plates are present and that there is no visible gap between them and the bottom surface of the carriage. You should be able to see a considerable gap between the plate and the bottem surface of the way.

Yes, you should be able to turn toward the tailstock without the carriage coming off the ways.

Robert D.

 

[cdhknives]

I don't think I'm communicating the issue properly. The carriage is not lifting off the bed, it is sliding front to back (but only the right side of the carriage is wobbling, the left side seems to be traveling down the bed in a straight line, hence my calling it 'snaking') causing the bit to dig deeper/shallower. I assume there is some way to tighten the carriage to bed contact surfaces but I don't see it. The R-L traversing wheel is also jumping, not rotating smoothly as the carriage progresses.

I zero the bit to the point of the live center in the tailstock before mounting the (roughly 2" diameter) block. The bit is a 1/4" HSS square blank sharpened in a slight curve (bull nose?) with plenty of undercut, held in the standard bit holder.

Remember that this lathe sat for 23 odd years before I got it. It was well cared for until then, but well used. I have been oiling, greasing, and cleaning for days up to this point, but storage damage has been found (dinged pulleys) already and more is a distinct possibility.

 

[4GSR]

wa5,

Your lathe has flat ways, and what is causing this is slack in the carriage as it rests on the bed. I'm not very familiar with the Atlas-Craftsman lathes but have worked with larger flat ways on larger machine tools in the past. There maybe a gib that will allow you adjust to take some of the slack out of the carriage to minimize and or eliminate the grooving effect you are getting. If I had to guess, there is probably a adjustable gib on the back side of the carriage that is held and adjustable with several screws very similar to that used on the cross slide. If the lathe does not have a gib to adjust the slack out, then you have to go to plan B. That is do some rebuilding work to fix the slack problem. Ken

 

[pdentrem]

On the back of the carriage, there is a gib that pushes against the side of the ways. if you look at the exploded diagrams available here and on other sites it is called 10F 57. There are 4 screws on the back that allows you to adjust the gib to get smooth running of the carriage. Check there first.

I hope that you are protecting the machine from the wood dust as the dust will absorb all the lube away from the running surfaces and you will be metal on metal pretty quick.
Pierre

 

[wa5cab]

Oh! In that case, you probably need to tighten the carriage gib. Look on the back of the carriage. You should see four slotted set screws, each with a lock nut. First, remove the right rear bed wiper and look in the space between the back of the rear way and the inner (front) surface of where the back of the carriage hangs over the way. Make sure that the gib is actually still in there. The gib is a piece of steel flat bar about (on your machine) 3/8" x 1/8" or so (I forget the exact thickness). It is held in place by four shallow holes that the adjustment screws bottom in. If it is still there, replace the wiper. If it isn't, don't move the carriage again until you find and install it.

Loosen the four nuts and tighten the four screws snug. Then back each one out (loosen) about a sixteenth of a turn and while holding the screw with the screwdriver so that it cannot turn, tighten the nut. Try to move the carriage with the handwheel. It should move freely. If there is noticable drag, loosen the nuts and back the screws out another sixteenth of a turn. You have to hold each screw with the screwdriver while loosening or tightening the nut to keep the screw from turning with the nut.

Once you have the carriage moving freely left to rignt but not able to move significantly front to back, use the handwheel to run the carriage toward the tailstock. At some point depending upon usage history it will probably begin to get tight. What you do next is a judgement call. If most of your work can be done with the carriage in the freely moving area, leave the adjustment screws as they are (if you ever need to remove the carriage from the bed you will have to loosen them). If you need more travel, loosen the screw nearest the tailstock just a little. Or if you think you must have quite a bit more travel, loosen all four screws, move the carriage to where it has to be able to go, and repeat the steps in paragraph 2.

However, the downside to doing this is that the work diameter is going to be slightly larger nearer the headstock than it is nearer the tailstock. The only actual fix is to have the bed ground. A workaround for some cases might be to machine the part to finish diameter at the tailstock end. Then flip the part end for end and take one more pass. Another possible workaround would be to set over the tailstock so that the part is the same diameter at both ends.

Robert D.

 

[cdhknives]

Thanks guys! I found the adjustment screws. I guess I looked right at them but didn't SEE them! Too busy today to work with it but I'll give it the adjustment cycle next time I'm ready to get greasy.