Ancient lathe chuck adjustment

Calling any machinists that might have experience with old lathes. I have an old Worcester lathe with a 3 jaw chuck (can't find any info on the chuck except the patent date). One of the jaws is out of sync with the others by about 5 thousands. Is there a way to adjust it? Keep in mind I'm a novice when it comes to machining...

Is it a scroll chuck?

I would say no. that old, in that condition, I would be surprised it's not out allot more. Have you tried turning the jaws in place ? make sure you preload them with a ring.

"Keep in mind I'm a novice when it comes to machining..." You guys are speaking Greek!

.005 is not much. suggest you dis-assemble it fully, clean very well, and take a flat file to every flat surface to get rid of any dings & humps. And then hard turn the jaws in place. Which....will only get it true in that one dia. setting. Or get a 4-jaw and learn how to dial them in.

Scroll means all three jaws move at one time a independent each jaw moves separately

Post some more photos showing how the jaws are opened/closed. I was looking for a square where the chuck key would fit but couldn’t see one. Scratch that. I see it now. DDoug said: suggest you dis-assemble it fully, clean very well, and take a flat file to every flat surface to get rid of any dings & humps. Click to expand... I think that might be a good start. It looks as though it could use some TLC.

pittsburgh cat man said: Scroll means all three jaws move at one time a independent each jaw moves separately Click to expand... I see. Yes the jaws all move together. When I put an indicator on each jaw base, two of them are within a thousandth, but the third is off from them. I thought maybe it was just the removable part of the jaw that was off but it is the base itself. It did come with another set of jaws.

DDoug said: .005 is not much. suggest you dis-assemble it fully, clean very well, and take a flat file to every flat surface to get rid of any dings & humps. And then hard turn the jaws in place. Which....will only get it true in that one dia. setting. Or get a 4-jaw and learn how to dial them in. Click to expand... Ok good idea, I will work on cleaning and checking it sometime when I get a chance. It seems like turning the jaws would help it be closer to true at all settings, because it's always the same one that is off, and it seems to be that way whether it's closed up or opened, and at various points in between. I would need to do it with the jaws in both positions though so it trues it up for both internal and external use. I did get a 4 jaw for it but it didn't come with a backplate, and I haven't been able to find a backplate with the same thread. I bought a blank backplate but I tried cutting some practice threads and the gears won't stay engaged so the threads get messed up. I think the lathe must be missing a part that locks the gears in place.

I see the jaws fix to the chuck with Allen screws. Is there any adjustment, however minimal that might be, on those screws.? Judging by the visible corrosion on the back side of the jaws, plus I assume similar on the front side of the chuck, a thorough cleaning of all the mounting surfaces might just get you the 5 thousandths you are looking for. As mentioned already by Doug

Nige said: Post some more photos showing how the jaws are opened/closed. I was looking for a square where the chuck key would fit but couldn’t see one. Scratch that. I see it now. I think that might be a good start. It looks as though it could use some TLC. Click to expand... Yes, the whole lathe needs some TLC. And I need to find someone that is familiar with this lathe to walk me through properly maintaining it.

I would be curious of what kind of run out you get on a piece of stock in the chuck

Nige said: I see the jaws fix to the chuck with Allen screws. Is there any adjustment, however minimal that might be, on those screws.? Judging by the visible corrosion on the back side of the jaws, plus I assume similar on the front side of the chuck, a thorough cleaning of all the mounting surfaces might just get you the 5 thousandths you are looking for. As mentioned already by Doug Click to expand... The jaws are located in the bases by little "donuts". The Allen screws just clamp them tight. I haven't tried loosening the bolts and using an indicator to check for movement, but based on how tightly they fit, I don't think there will be any. Perhaps this gives a clue about the way this chuck was treated in the past... Meanwhile, I've found another solution for getting the gear centered on the lathe:

That is a scroll type 3 jaw. It is set up with master jaws and top jaws, bolted on, which can be hard or can be soft, with the intent of machining them as mounted, for specific diameters or to have shoulders for depth stops. This applies to soft jaws used for internal or external workholding. Very little runout can be achieved this way, as well as accurate repeatability. It is not at all unusual to have some runout using hardened top jaws in a 3 jaw chuck. Especially one that age. You would do well to ignore the indicator readings on the jaws themselves, however. In function, what matters is how well the part or stock is held. Your hard jaws can be checked by chucking an object that is round, and the indicator run on some precision surface. I use a bearing race of a suitable size if I need to check. This will "load" the scroll/master jaw interface and tell you what the runout is. Normally, for a part to be turned or bored, rough stock is placed in the 3 jaw and the part is machined complete and parted off, when possible. The result is runout between features is as good as the bearings in the headstock. Only in the case of chucking a part for a second operation, or an existing part to be modified or repaired (thread chasing, for example) is the typically minor runout of a 3 jaw really critical. I'll agree that a bit of TLC could be beneficial, but I don't see it really helping with your problem. Also agreed is that boring or turning the jaws will have a greater effect only at that point in the scroll rotation, with the potential being significantly adverse at any other point in the scroll rotation. Proceed with care. Those master jaws are typically quite hard and even carbide can struggle. It is more common to grind the jaws with a tool post grinder should that become necessary. Be sure and load the jaws in case you do go that route.

pittsburgh cat man said: I would be curious of what kind of run out you get on a piece of stock in the chuck Click to expand... I'll have to check next time the chuck is on.

Tony Wells said: That is a scroll type 3 jaw. It is set up with master jaws and top jaws, bolted on, which can be hard or can be soft, with the intent of machining them as mounted, for specific diameters or to have shoulders for depth stops. This applies to soft jaws used for internal or external workholding. Very little runout can be achieved this way, as well as accurate repeatability. It is not at all unusual to have some runout using hardened top jaws in a 3 jaw chuck. Especially one that age. You would do well to ignore the indicator readings on the jaws themselves, however. In function, what matters is how well the part or stock is held. Your hard jaws can be checked by chucking an object that is round, and the indicator run on some precision surface. I use a bearing race of a suitable size if I need to check. This will "load" the scroll/master jaw interface and tell you what the runout is. Normally, for a part to be turned or bored, rough stock is placed in the 3 jaw and the part is machined complete and parted off, when possible. The result is runout between features is as good as the bearings in the headstock. Only in the case of chucking a part for a second operation, or an existing part to be modified or repaired (thread chasing, for example) is the typically minor runout of a 3 jaw really critical. I'll agree that a bit of TLC could be beneficial, but I don't see it really helping with your problem. Also agreed is that boring or turning the jaws will have a greater effect only at that point in the scroll rotation, with the potential being significantly adverse at any other point in the scroll rotation. Proceed with care. Those master jaws are typically quite hard and even carbide can struggle. It is more common to grind the jaws with a tool post grinder should that become necessary. Be sure and load the jaws in case you do go that route. Click to expand... Thanks for the info and advice. Most work I do with this is on existing parts. I do hope to be able to get the 4 jaw backplate figured out so that I can use it someday. I know it would be a better option for some things I do.

Your tasks will dictate your tools. If you can get the 4 jaw mounted, at first you may spend a bit of time dialing in your work, but that will quickly become routine and can be as accurate (or not) as needed. From the chuck wrench, I would say there are a couple of possibilities. The scroll could be distorted at some point from over-tightening, and the jaws (most likely) will display a bell-mouth condition. This most often results from the chuck being over-tightened with a piece that only sits a little ways into the jaws and there is nothing under that master jaws deep in the chuck. The body will yield and the face of the chuck becomes slightly conical to some degree. Nothing can be done, to my knowledge, about the body, but the bell-mouth condition can be remedied by the same grinding or boring as for runout. In production shops, soft jaws are considered either consumables, and machined for each part-batch that comes along, or dedicated fixturing that is kept as a kit for repeat orders. They aren't usually costly. Your chuck using those hollow dowels should not really have appreciable movement. There are always keys or pins, or even serrations to take the radial stresses at the jaw-jaw connection.

materthegreater said: Thanks for the info and advice. Most work I do with this is on existing parts. I do hope to be able to get the 4 jaw backplate figured out so that I can use it someday. I know it would be a better option for some things I do. Click to expand... Even if you need someone to stop by and thread that 4 jaw backplate for you, it will be worth it. Working on repairing parts more often than not will be much easier with a 4 jaw. Dialing one in is easy skill to learn. Number the jaws 1-4 to keep track as you turn the chuck by hand and watch the indicator.

I bought a Bison chuck for a small lathe I owned. After 25 years The chuck needed some truing. I rigged up a Dremel grinder on the tool post and lightly ground the gripping faces of the jaws. The bent aluminium rods hold the jaws tight against the scroll plate. I made several very light passes with the grinder. I'm very happy with the result. A good cleaning afterwards to get all the abrasive grit off the machined surfaces.

I would like to see more pictures of your lathe. What gears are not staying engaged. I see a Zerk/Grease fitting on the headstock bearing. There is an oilier you can get to lube the bearings they should not be greased. Originally your lathe probably had little glass oil dropper on both headstock bearings. 32 wt hydraulic oil is what I use on my lathe and mill. I am guessing the spindle thread is 2 1/4" x 8. If so you should be able to buy an adaptor and machine it to fit your 4 jaw chuck. Here is some history on your lathe: Worcester Lathes Founded by the former president of Whitcomb-Blaisdell Machine Tool Co. around 1910, the Worcester Lathe Company was based, along with many other machine-tool makers, in the state of Massachusetts . A range of regular engine-type machines was made, in both www.lathes.co.uk