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3 jaw chuck scroll

swellwelder

Stainless
Joined
Sep 21, 2002
Location
Valley City, ND USA
I took apart a 3 jaw chuck to give it a thorough cleaning, and due to my lifelong desire to know how did they do that, started wondering how is the spiral scroll machined? That and the jaws themselves. I can see that some kind of rotary table must be used, and it must be connected to something to move it in sequence with the cut, but the details would be nice to know!

Dale Nelson
 
I think the scroll can be machined easily on a lathe. Set the feed for threadcutting, but engage the crossfeed instead of the longitudinal feed.

Don't know for sure though.
 
It would be quite tricky to do a spiral on the lathe, since there is no surefire way to force the tool to repeatedly track in the same groove.

If I had to cut one, I think I'd use a universal dividing head, tilted up at 90 degrees, in rotary table attitude. Then, the dividing head rotation would be driven via a gear train that got its power from the X screw of the table. A suitable selection of compound gearing would be used to achieve so and so many revolutions of the scroll plate, per inch of table travel.
 
My dad said he worked in a place in London once and he said a guy there would machine scrolls on a Meuser Lathe. He said there was a special gear set up between the leadscrew and crossslide and you did a operation similar to threading.Maybe somone else can add to this as I've never seen a machine with this set up.Martin
 
I have never seen a scroll machined, nor have I any knowledge of how it was done. It is an interesting subject which has had me thinking about it at odd moments over the years- usaully when I use a scroll chuck or clean/main tain one .Thinking it over, I wonder if the following setup might work:

-If a shop had to make one or two scrolls, they could use an adaptation of the setup for milling helical flutes or a worm on a horiztonal milling machine. In this method, the table feed and the dividing head are connected by gearing so that the table advances for the lead of the helix, while the gearing from the table feed screw turns the divinding head. For milling a scroll, the same concept should work. A very similar setup would be used, only the milling machine would need to have a vertical spindle, and a rotary table would be used to mount/revolve the scroll blank. The "X" Axis feed screw would be geared to a rotary table on a vertical mill, table's worm shaft and the "X" axis feedscrew. As the "X" axis feedscrew turned, it would advance the scroll by the lead of the "thread", while causing the rotary table to revolve. An set of end mill cutters ground for roughing and finishing the scroll "thread" would be likely needed. Cinncinnati and Brown & Sharpe milling machines had the capabilities for this sort of gearing to connect a dividing head and "X" axis feedscrew for helical milling.

-If a shop were in production of scrolls, as for the manufacture of chucks, I would imagine they would have a dedicated milling machine setup for the purpose. Cutting a scroll in a lathe would require numerous passes with a single point tool. If a lathe were wanted for the porduction of scrolls, a "tee bed" lathe might have been ordered. A "tee bed" lathe was built for specialized work, usually done on a faceplate. The bed laid at 90 degrees to the spindle, and it had a carriage, cross-slide & compound as a regular engine lathe would. With a lead screw geared off the spindle, but the bed laid at 90 degrees, a "tee bed" lathe could have been used for making scrolls.

Vertical turret Lathes and Vertical Boring Mills pretty well did away with the need for tee bed lathes.

-FWIW: At Brooklyn Technical HS, there was a separate little toolroom type of shop which was off limits to most students. It was in the charge of a cantankerous teacher, who was in truth, a fine toolmaker. He had the job of making jigs and fixtures, making instruments and test fixtures, and repairing all manner of finer stuff. This particular guy had his little inner sanctum which he only let a favored few students into. I was not part of the favored few, so did not get into the inner sanctum. On towards my senior year, that oldtimer softened up slightly towards me, and let me take a look at his private toolroom. Amongst other machine tools, there was a Rivett bench lathe that "looked old". It was like no other bench lathe I had ever seen. It looked to have a bedway on the vertical front face of the bed aswell as on the top of the bed, and had loose change gears. The oldtimer explained it was a special lathe which had the ability to cut scroll threads. I never saw it set up for the purpose.

OTOH, we had the good fortune to have another ex toolmaker as our regular shop teacher in our junior and senior years. This teacher was named Ivar Alskog. Mr. Almskog was one of the finest men I have ever known, any way you took him. He was a fine toolmaker who had returned to his alma mater to teach after years in industry. Mr. Almskog took a genuine interest in us kids and taught us shopwork as well as something of life as we approached our adult years. By today's standards, I suppose Mr. Almskog would be called on the carpet. He was an upright man who kept a worn copy of the Machinery's Handbook and an equally worn Bible on his desk. He had the patience of a saint with us kids. From the way he worked, and the fact he never seemed stumped, you had the feeling he could probably make anything if you handed him an idea or sketch and turned him loose in a machine shop. The machine shop classroom we were in was equipped with geared head Hendey engine lathes, probably about 14" x 50" between centers, LOO tapered spindles. These lathes were driven off the overhead lineshafts. SOme of the shops at 'Tech had been refitted with(then) brand-new LeBlond Regal engine lathes. As kids in the Mechanical Course, some of us looked at the older Hendeys and thought we were getting the short end of the stick. Mr. Almskog heard the mumblings and explained to us that the Hendey lathes were some of the finest engine lathes ever built. He said he had done all manner of off the wall jobs on a Hendey, including cutting multiple lead threads and gauge work. He showed us a relieving attachment and gearing for the Hendey engine lathes, though we did not use it. I had gotten to talking to Mr. Almskog about the Hendey lathes and he showed me an old Hendey manual with a picture of Henry Hendey in the front flyleaf. Mr. Almskog told me that Hendey used to build lathes to order for production work, as well as making up all manner of attachments for their lathes to special order.

It would not surprise me if Hendey offered a train of gearing to connect the cross slide to the spindle in the manner of a lead screw for threading of scrolls. With the type of gearing and drive shafting they already had in production for their relieving attachments, it would not be too much of a stretch of simply provide a spiral or bevel drive to the cross feed screw.

The methods for machining a scroll produce a scroll out of a soft steel blank. For use in a chuck or similar, a scroll is usually hardened and ground. Grinding down into a "face" thread or continuous narrow groove has got to be an equally interesting proposition. I wonder if the hardened scrolls were then setup on the same type of milling machine/rotary table, only with a high speed grinding spindle mounted on it.
 
Joe, I think you are right on about Hendey making a lathe that could do this job. They and Lodge and Shipley had what was called a "coarse threading" attachment, which simply was an overdrive for the leadscrew, turning it faster than the spindle for extraordinarily long leads.

They also had the "spindle speed reducer", which was a headstock mounted gearbox that was a 6:1 reduction unit for the spindle. On an old lathe like a Hendey or L&S with double digit low speeds, this could give a low speed of 2-3rpms. Between the two acessories, some pretty neat stuff could be done.

As for the scroll, L&S and Hendey also explain how to convert feed on the crossfeed into a scroll thread. The only thing is that the spindle or leadscrew must be reversed with the feed engaged to maintain the location of the start. No thread dial on the feed handle.

If the speed reducer were used, the spindle would have to be reversed, as even the reverse-to-leadscrew would not work due to the 6:1 reduction placing the spindle in a different place, even if the single tooth leadscrew dog aligned correctly.

Assuming you had all this worked out, the actual single point threading shouldn't be too difficult. You would have to start with a depression in the center the depth of the thread and probably and inch or so in diam. From there on it would be just like cutting any other thread, except the spindle would be reversed to return and the feed would remain engaged the whole time. Add the fact that you would be working at 90 degrees to the usual thread, so I imagine the compound would be set accordingly.
 
Hello Guys!! I am new to this website. I was just going through this interesting thread. I would like to mention here that I am actually manufacturing high precision 3 -4 - 6 jaw chucks in India. Would love to answer any of your technical questions as far as I can or any trade inquiries that come up.

Also can anyone suggest me good sources for chucks trading in South Africa, Europe and USA. It will be really helpful!!

Cheers
@RjUn
 
It would be quite tricky to do a spiral on the lathe, since there is no surefire way to force the tool to repeatedly track in the same groove.

If I had to cut one, I think I'd use a universal dividing head, tilted up at 90 degrees, in rotary table attitude. Then, the dividing head rotation would be driven via a gear train that got its power from the X screw of the table. A suitable selection of compound gearing would be used to achieve so and so many revolutions of the scroll plate, per inch of table travel.

I have never tried this method, but I think you might be able to keep the transverse axis feed engaged and just reverse the motor to get back to the starting point. I have used a similar method to cut metric threads on a lathe with an american leadscrew.
 
I have never tried this method, but I think you might be able to keep the transverse axis feed engaged and just reverse the motor to get back to the starting point. I have used a similar method to cut metric threads on a lathe with an american leadscrew.

I know this is a necropost, but I was curious and tried it on a piece of scrap. For posterity's sake, it works:
Ghetto Scroll.jpg
 
I think lathes could make a scroll within a few tenths, but if hardening was needed then grinding would likely finish the work.

If one made the scroll to R 43 to 48 carbide tooling could likely make a decent scroll on a lathe..but like Joe Michaels mentioned it would likely take a special lathe,

A low-priced throw-away scroll might have been a good idea back when people fixed things rather than throwing things away... yes then put in the replacement and add a shim to go around.
 
Chuck jaws are hardened and ground, so I expect the scroll to be, though I've never tested one. Wouldn't make much sense to put them against a softer scroll.
 
Since we are discussing this, how accurate do you think your typical lathe cross-feed gear reduction is vs CNC interpolation? Obviously much depends on the machines in question, but you can get air turbine grinding spindles for a CNC, so if you needed a one-off part to fix a lathe chuck, it seems like you could make it happen. If using a lathe, you could use a toolpost grinder on your lathe to accomplish the same result (please, no comments to the effect of "don't use a toolpost grinder ever"). I'm not claiming these are suitable methods for production parts, nor even necessarily that making a scroll yourself is a good idea, I'm just curious as to what more seasoned professionals think about the two low-budget options for a one-off part.
 
One could have a master and a double spindle so being a tracer machine (grinder).
Most scrolls are hard and so the chuck body takes the wear.
to restore one might throw away the chuck body and keep the scroll.

it would likely be a task to male a scroll near the quality of one that comes in a common chuck.
 








 
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