Lathe chuck mounting standard?

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VelocityDuck
Posts: 41
Joined: Mon Dec 07, 2020 6:14 am

Lathe chuck mounting standard?

Post by VelocityDuck » Fri Mar 26, 2021 10:06 am

Are there standards for chuck mounting?

I want to get a 4-jaw for my 3-in-1. It's Chinese origin so it (appears) to be metric. The mounting plate inset is 100mm in diameter and the mounting bolts are M8-120 on a 100mm pattern. I would like to get something that bolts on without having to make an adapter. I haven't started looking, but I'm wondering if there are standards (like R8, 5C or MT) for lathe chucks.

My current 3-jaw.
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pete
Posts: 2169
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Re: Lathe chuck mounting standard?

Post by pete » Fri Mar 26, 2021 1:32 pm

Yeah there's probably standard chuck back plate mounting dimensions somewhere. And if there anywhere they'd probably be under the German DIN system that are usually recognized by most other manufacturer's world wide. And the Germans seem to have standards for almost everything. :-) But there also not law so there optional for any manufacturer to follow or not as they see fit. Your picture only shows the chuck recess, that's about the least important dimension. What's the actual lathe spindle mount? If it's a common one then what are called semi finished back plates are available with those the important dimensions to fit the spindle are already done and you do some rudimentary machining to fit the actual chucks recess and bolt pitch circle your going to use and it's dimensions.

This is being factual from past personal experience and not China bashing. I don't think any world wide chuck standards could be trusted on the cheaper chucks if they were even building them to those. These lower end chucks are made to meet the price point and repeatable accuracy on important dimensions are of far less importance. The better chuck manufacturer's do list the chucks dimensions to be used when fitting back plates, but you'd need to spend multiple times more for any of those better brand name chucks. Even then I'm still going to measure what I have and fit to that.

But you weren't expecting to use one back plate for both the 3 jaw you already have and whatever independent 4 jaw you get were you? I can't think of anyone who would do so. Back plates to fit your lathe spindle mounting dimensions are simply semi permanent adapters to go from a plain back chuck and have them fit what the spindle mount requires. There are direct fit chucks that don't use a back plate at all because the mounting requirements to fit the spindle are machined directly into the chuck body itself. With the separate back plate method and a change in lathe owner ship, you can then re use the same chucks with a different spindle mount just by machining and adding a new back plate to fit the different lathe with out buying all new chucks. If your spindle mount is something common, then 4 jaw independent chucks should be available from the manufacturer and possibly others that are usable right out of the box. In my opinion machining your own back plates on the machine there to be used on is always going to be a bit more concentric than something off the shelf. That's maybe a bit less important with a 4 jaw, but still something to be considered.

VelocityDuck
Posts: 41
Joined: Mon Dec 07, 2020 6:14 am

Re: Lathe chuck mounting standard?

Post by VelocityDuck » Sun Mar 28, 2021 9:01 am

Oh well. I figured that since it uses R8 collets for the mill and Morse Taper for the tailstock that there was a chance.
But you weren't expecting to use one back plate for both the 3 jaw you already have and whatever independent 4 jaw you get were you?
It seemed like a reasonable assumption.
If your spindle mount is something common, then 4 jaw independent chucks should be available from the manufacturer and possibly others that are usable right out of the box.
They list 4-jaw chucks but they also say that for the ones they sell, an adapter plate will need to be made to use on my lathe.

I've looked around at writeups and videos on making adapter plates. Some use steel and some use aluminum. Can you really get away with aluminum?

This is the spindle on my lathe. Raised part is 100mm and the outside diameter is 130mm (no idea why it posts upside down).

Thanks for the guidance.
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John Evans
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Location: Phoenix ,AZ

Re: Lathe chuck mounting standard?

Post by John Evans » Sun Mar 28, 2021 1:04 pm

Well you are a bit screwed as that 3in 1 uses a non removable chuck mount ! As I see it your only answer is most likely is to make a adapter plate. You have a 3 bolt pattern and 4 Jaw chucks will have a 4 bolt mount . For that light duty machine I think aluminum would work OK.
www.chaski.com

pete
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Re: Lathe chuck mounting standard?

Post by pete » Sun Mar 28, 2021 4:19 pm

It's a standard 3 stud mount with a step as the back plate locator. I have a slightly modified version of that method on a couple of my lathes. And it's one of the easiest to machine a back plate to fit. Since the mounting studs always stay permanently fixed to the back plate, then fitting a 4 jaw even if it requires 4 mounting bolts is also easy just by using 4 cap screws counter sunk into the back plate and screwed into the rear of the chuck. If it's a front mounted chuck design, then your chuck mounting bolt locations would need to be carefully off set from the stud locations. I'd also use something like a single edged old school razor blade and scrape what looks to be either light rust or old oil off that spindles mounting face. Any irregularities no matter how small will give you a serious wobble on the face of the chuck. Keeping that surface and the back plates surface that fits to it spotlessly clean and burr free are one of the more important ones on your lathe. And raw cast iron back plate castings aren't hard to source from multiple tool suppliers. This post viewtopic.php?t=80503 saves me re-typing why cast iron is the better choice over anything else. Even my cheaper off shore 3 & 4 jaw chucks came with cast iron back plates as well as there face plates being made from it.

Measure as accurately as possible that step on the spindle face and the bolt hole pitch circle. With those dimensions known it should then be easy enough to find either 4 jaw independent chucks with the correct back plate or just pre machined back plates to fit what you already have. That spindle mount is actually one of the more common one's used on a lot of the off shore machines. I'd be surprised if direct fitting chucks with back plates or just the back plates weren't readily available. And if you really can't find one off the shelf, then those unfinished back plate castings are the next obvious choice. If the factory did use proper DIN standard dimensions for the bolt pitch circle and that step on the spindle face? Then something from here https://littlemachineshop.com/products/ ... back+plate just might work. Even the correct extra studs you'll need should also be available although those aren't hard to make either since the factory one's don't seem to be properly heat treated.

LIALLEGHENY
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Location: Bohemia, NY

Re: Lathe chuck mounting standard?

Post by LIALLEGHENY » Wed Mar 31, 2021 12:49 am

Who is the manufacturer of the lathe and the model? Can you take a picture looking between the headstock and the chuck mount?

Nyle

VelocityDuck
Posts: 41
Joined: Mon Dec 07, 2020 6:14 am

Re: Lathe chuck mounting standard?

Post by VelocityDuck » Wed Mar 31, 2021 7:44 am

Shoptask Bridgemill.

There's really nothing to see. The chuck mount is part of the spindle that goes into the headstock.

Profkanz
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Joined: Mon Dec 04, 2017 9:14 am

Re: Lathe chuck mounting standard?

Post by Profkanz » Sun May 02, 2021 11:27 am

Although I have a South Bend lathe, before I had multiple chucks and collets I made an R8 collet adapter to use with a through the spindle drawbar. You could do the same by mounting a chunk of 4 inch round stock and boring it out to the collet OD, and then cutting the taper with the compound rest and a boring bar. R8 collets are available in 1/32 steps up to at least 3/4 inch. I also have collets at 7/8 and 1 inch.

armscor 1
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Location: Philippines

Re: Lathe chuck mounting standard?

Post by armscor 1 » Sun May 02, 2021 4:18 pm

I have similar spindle on my lathe, it did not come with a 4 jaw chuck, purchased a 100 mm 4 jaw chuck but had 4 tapped holes instead of three, simply tapped 3 new holes and bolted directly to spindle, register fitted perfectly.

TomB
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Location: Southern VT

Re: Lathe chuck mounting standard?

Post by TomB » Sat May 08, 2021 10:52 am

I have that lathe and both 3 and 4 jaw chucks for it. The lathe came with the 3 jaw and options I could have added to include the 4 jaw plus I don't remember what. I did not buy the options but latter found I wanted the 4-jaw and called JT at Shopmaster and for about $100 he shipped a 4-jaw chuck. To switch between the two chucks I take out the 3 screws, pull the chuck slightly and the mounted chuck comes off in my hands. The chuck going on is then guided onto the slip fit machined into the round mount on the lathe axis. Once the next chuck is pushed on the boss I can spin it to bring the tapped holed in the chuck into alignment with the slip fit holes in the headstock axis. The fact that the lathe has MT2 mounting is not relevant to the interchange of chucks. The MT2 mounting surfaces are inside the lathe headstock axis and the chucks never come in contact with them.

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