Need help with my metal lathe

JC

JC

Coos Cues
I have an old jet lathe and it's the first metal lathe I have ever worked with. I do not come from a machinist background.

When I first bought it I ground the jaws to near dead center on the chuck. It still has about 2 thou run out with 16 inches of hardened shaft poking out at the far end. It's always been about like this since I worked the jaws.

The tailstock has always seemed in good alignment. I could put a 3 point carbide drill in and drill a hole in wood, take the bit out of the tailstock chuck and turn it around and it would be a nice snug fit into the hole it just drilled and spin dead nuts like this.

Then one day I notice my hole was oversize from the bit. Thought it was the bit and tried another with the same result.

So i bought a machined rod made for aligning the tailstock between dead centers and it was a couple of thou off side to side and a couple of thou low in the front of the tailstock. So I made appropriate adjustments until the test rod was dead on end to end side to side and up and down. I even tried the razor blade between the points and it's damned near straight in every direction.

But when I step drill a hole it's way oversize. I mean .040" with a .500" bit. The same bit I used to be able to reverse and slide in with friction into the hole I just drilled with it. I have always relied on this lathe to drill certain holes dead on with just 3 point stubby carbide bits but now I have to pretty much bore everything. I have tried tightening the quill enough so it's snug while extending.

I would like to figure out what the problem I'm suddenly having is. The lathe didn't have any trauma due to clashing anywhere from a screw up or anything like that. It just one day wouldn't drill a tight hole any more.

Can any of you machinists set me in the right direction to get this thing squared away? I can't figure how it can be so out of alignment and not show it with a dial indicator.

Thanks
 
JC said:
I have an old jet lathe and it's the first metal lathe I have ever worked with. I do not come from a machinist background.

When I first bought it I ground the jaws to near dead center on the chuck. It still has about 2 thou run out with 16 inches of hardened shaft poking out at the far end. It's always been about like this since I worked the jaws.

The tailstock has always seemed in good alignment. I could put a 3 point carbide drill in and drill a hole in wood, take the bit out of the tailstock chuck and turn it around and it would be a nice snug fit into the hole it just drilled and spin dead nuts like this.

Then one day I notice my hole was oversize from the bit. Thought it was the bit and tried another with the same result.

So i bought a machined rod made for aligning the tailstock between dead centers and it was a couple of thou off side to side and a couple of thou low in the front of the tailstock. So I made appropriate adjustments until the test rod was dead on end to end side to side and up and down. I even tried the razor blade between the points and it's damned near straight in every direction.

But when I step drill a hole it's way oversize. I mean .040" with a .500" bit. The same bit I used to be able to reverse and slide in with friction into the hole I just drilled with it. I have always relied on this lathe to drill certain holes dead on with just 3 point stubby carbide bits but now I have to pretty much bore everything. I have tried tightening the quill enough so it's snug while extending.

I would like to figure out what the problem I'm suddenly having is. The lathe didn't have any trauma due to clashing anywhere from a screw up or anything like that. It just one day wouldn't drill a tight hole any more.

Can any of you machinists set me in the right direction to get this thing squared away? I can't figure how it can be so out of alignment and not show it with a dial indicator.

Thanks
Click to expand...
You are using dead centers to check alignment and drilling with a chuck in the tailstock. Check the chuck with a radial indicator or try another chuck.

Cory
 
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Sometimes old lathe have a lot of wear on bed and it can change height at different spot, but it probably not this fact...
 
<===Only a hobby machinist.

That's weird to be off that much, when everything was true before. Could there be a burr on the morse taper of the chuck or the morse taper inside the tailstock? Maybe put a dial test indicator in the headstock chuck and put the indicator tip inside the tailstock morse taper. Try it at a few different depths inside the tailstock. If that checks out, then try another chuck in the tailstock. Or put an oilstone to your chuck's taper to knock down any burrs.
 
Could it be as simple as your drill chuck is worn? Those chinesium chucks will wear a lot quicker than a Jacobs or Albrecht.
 
Kim Bye said:
Could it be as simple as your drill chuck is worn? Those chinesium chucks will wear a lot quicker than a Jacobs or Albrecht.
Click to expand...
I'm using the same Jacobs chuck that came with the lathe but it has come loose and spun a few times.
 
If you get a new chuck, I used to work in a toolroom that supported a manufacturing plant for a couple years part time in 1999/2000 and they had Albrecht chucks on every machine. We had something like 10 Bridgeports and 10 Hardinge toolroom lathes. At home I had a Bridgeport mill and a chinese no-name lathe. I had brand new Jacobs ball bearing super chucks on them at home, but they were nothing like the toolroom Albrecht chucks. A couple years later I ordered and tried the knockoff chinese brand chucks that looked like the Albrecht. I think they were about $100 (Albrecht being about 300-400). They were excellent. Way, way, way better than the Jacobs bb super chuck. And about as good as the Albrecht as far as I could tell. Fast forward to my RD dayjob that had just 2 lathes and one mill, and I bought the knock off Albrechts for all of them. They got used for 10 years and held up really well. I'd get the knockoffs again.
 
iusedtoberich said:
If you get a new chuck, I used to work in a toolroom that supported a manufacturing plant for a couple years part time in 1999/2000 and they had Albrecht chucks on every machine. We had something like 10 Bridgeports and 10 Hardinge toolroom lathes. At home I had a Bridgeport mill and a chinese no-name lathe. I had brand new Jacobs ball bearing super chucks on them at home, but they were nothing like the toolroom Albrecht chucks. A couple years later I ordered and tried the knockoff chinese brand chucks that looked like the Albrecht. I think they were about $100 (Albrecht being about 300-400). They were excellent. Way, way, way better than the Jacobs bb super chuck. And about as good as the Albrecht as far as I could tell. Fast forward to my RD dayjob that had just 2 lathes and one mill, and I bought the knock off Albrechts for all of them. They got used for 10 years and held up really well. I'd get the knockoffs again.
Click to expand...
Can you link where I may purchase one?
 
John, is the barrel tight in the tailstock housing?

There should be a set screw that keeps the barrel from rotating. If this is too loose, the barrel can creep up a bit if the tolerance is not tight. Or, if the screw is too tight, it can bind. Higher quality lathes have a keyway.

Put a ground rod in the drill chuck and put an indicator on the chuck or faceplate and wind in the tailstock and see if the indicator moves. If so, the chuck is not moving in perfectly straight.

Rob.
 
First and foremost, in my experiences...what is the lathe sitting on? If a wood bench....many weird things will happen as the seasons change.. a solid metal bench will stay very stable, a wooden bench...even very solid, can move and twist the bed and throw the alignment off a .001 or 2, or even larger....which will explain what you are experiencing. Even after being good for years, have seen this suddenly become an issue. Good luck tracking it down
 
robbycar said:
John, is the barrel tight in the tailstock housing?

There should be a set screw that keeps the barrel from rotating. If this is too loose, the barrel can creep up a bit if the tolerance is not tight. Or, if the screw is too tight, it can bind. Higher quality lathes have a keyway.

Put a ground rod in the drill chuck and put an indicator on the chuck or faceplate and wind in the tailstock and see if the indicator moves. If so, the chuck is not moving in perfectly straight.

Rob.
Click to expand...
Dave38 said:
First and foremost, in my experiences...what is the lathe sitting on? If a wood bench....many weird things will happen as the seasons change.. a solid metal bench will stay very stable, a wooden bench...even very solid, can move and twist the bed and throw the alignment off a .001 or 2, or even larger....which will explain what you are experiencing. Even after being good for years, have seen this suddenly become an issue. Good luck tracking it down
Click to expand...
The barrel has a dowel at the bottom that runs in a groove and it was very worn when I bought it. I rebuilt the male part with weld and ground it back down to make it tight again. I have run the quill in and out and the alignment stays the same.

It's a toolroom lathe that has it's own dedicated steel bench. I leveled it when I set it up and it appears to still be level.

I am going to check the chucks closer today when I have time. Since the dead center is dead nuts to the headstock the answer must be lurking there somewhere. I bought an mt2 reamer from Russia off e-bay a couple of years ago and have never used it. Not sure I know how whether I should put it in the headstock under power or try cleaning up the bore by hand. It appears to be rough in there from various chucks spinning in it over the years.
 
Thanks for all the help guys. I found the problem with with the inside bore of my tailstock. I reamed it with the mt2 reamer I almost forgot I had and used another chuck with a pristine taper on it and my lathe is back to cutting straight again.

I knew the instant I tried my first test hole and heard the familiar squealing of the bit it was going to be a tight hole.

Not sure what happened in the hole but the reamer brought out some metal when I reamed it. Must have been a burr in there.
 
JC said:
Thanks for all the help guys. I found the problem with with the inside bore of my tailstock. I reamed it with the mt2 reamer I almost forgot I had and used another chuck with a pristine taper on it and my lathe is back to cutting straight again.

I knew the instant I tried my first test hole and heard the familiar squealing of the bit it was going to be a tight hole.

Not sure what happened in the hole but the reamer brought out some metal when I reamed it. Must have been a burr in there.
Click to expand...
One good habit to get into.........well actually a couple good habits.
I always keep something in the tailstock bore.....if I drill and don't want to leave the drill in it, I remove the drill and immediately install the live center back into it.
Second is I always wipe off the MT with my hand before I install it. Just peace of mind that I'm wiping any debris off before the install.
I also occasionally will shoot some air inside the bore before an install.
Over time, even the smallest particles can build up in the bore. If I feel the need I will use the MT reamer, by hand only, and give it a couple twists in the bore followed by a blast of air to dislodge any possible debris.
 
If your chuck has spun a few times, you probably will need a mores taper reamer to clean up the taper. You can try and do it without, by using some 400 to 800 wet and dry around your chuck taper, may work, but probably not if it galled up a lump in there. Your drill chuck taper should clunk in tight, with very little effort. If you have to pop it in hard to attempt to get it seated, it's either dirty or something is wrong. Taper reamers are fairly inexpensive, I think maybe $25-$30 for a #2.
 
With big heavy tailstocks the drill bit works like a boring bit if the tailstock or drill chuck either one is off center thus creating a larger hole.
For exact holes drill undersized and then use a reamer. Or just bore everything with a boring bar.
 
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