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Getting the proper chuck size

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Creativechipper

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#1
I am thinking of adding a 4 jaw chuck to my toolbox.

Looks like lots of size options, tapers, thread count, back plate, .etc, looks confusing to me.

I know my lathe has a spindle bore of 1.02" and a MT4 spindle taper.

What critical size, thread count info do I need to know before getting a new chuck?

Thanks
 

ttabbal

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#2
You need to know the chuck mounting information. It's specific to the lathe. The taper and bore don't help you. If you post your model number, I'm sure we can figure out what you need though. Another option would be to remove the chuck and take pictures and measurements of the mounting features.
 

dlane

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#3
Mounting info and lathe size ?
 

BaronJ

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#4
What size was your machine originally supplied with ? It should tell you in the handbook.
 

RJSakowski

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#5
If you still the Weiss, the manual states that you have a flange mounting with three studs and nuts. This is not a common mount and you may have to make a custom backing plate. DRO Pros carries the Weiss machines and should be able to sell a four jaw chuck for your lathe.
 

projectnut

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#6
Personally I would go with a chuck slightly smaller than the advertised "throw" of the machine. Rule of thumb says not to extend the jaws more than 3/4" beyond the body. If you have a machine with a 10" throw the maximum size chuck I would buy would be 8". With the jaws extended the 3/4" you would be swinging a 9 1/2" diameter piece.

The chuck and backplate are usually purchased separately. You can either buy a backplate with the proper mounting features for your lathe spindle and "finish" it to fit the chuck you buy, or buy a "blank" and make both the chuck and spindle mounting features. I have never been able purchase a backplate with the proper spindle features for any of my lathes. I just purchase blanks and make my own.
 

Creativechipper

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#7
It is a
Weiss WBL250F 10" x 30" Metal Lathe

I was looking at the specs for it off DRO's web page but did not see any other specifics than MT4 spindle taper and 1.02" spindle bore.

Just trying to learn how to tell and what info is important in relation to a new chuck.

Thanks!!
 

mikey

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#8
You need a 5-6" chuck. You can buy cheap Chinese chucks with the 3-bolt mount from LMS, Amazon or ebay or you can use a 3-bolt back plate and mount any plain back chuck to it. I don't know of any maker of high quality chucks that makes one that directly mounts to your spindle.
 

Creativechipper

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#9
Oh no, no good quality chucks..lol Thats ok I dont have the budget for a good one, I am sure its well over my budget.
But I do like quality tools and often buy used to get a better tool for my money.

Thanks , good info.

What is involved with finishing the mounting features of back plates and chucks?
 

Bob Korves

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#10
Oh no, no good quality chucks..lol Thats ok I dont have the budget for a good one, I am sure its well over my budget.
I think Mikey's post was not so much about the chuck quality you purchase as it was about the inability to be able to purchase a one piece chuck assembly, complete with backing plate, ready to purchase and immediately bolt it on and put it to work. There will be "some assembly required..."
 

Creativechipper

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#11
Some assembly required is better than batteries not included..lol
 

francist

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#12
Looks like DRO Pros has a 5" 4-jaw and backing plate they offer as an option for the WBL250F lathe. Wonder if they sell them separately from the lathe.

image.png
 

mikey

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#14
What is involved with finishing the mounting features of back plates and chucks?
Basically, you find a back plate that fits your spindle like the one RJ found on ebay. Then you find a chuck to match the size of the back plate. Depending on where the mounting holes are drilled in the chuck, this will be either a 5 or 6" chuck. You need to mount the back plate to your spindle and then machine the face of the plate to match the features found in the back of the chuck you need to mount. Most commonly, there will be a recessed area in back of the chuck so you need to machine a snout on the back plate that will fit inside this hole. Note that once you start to machine the plate, you do NOT remove it from the spindle until you're done. This assures that any machining you do will be as accurate as your spindle.

There are several schools of thought about the fit of the snout in this hole. Some feel you need a press fit and will make the snout (called a register) half a thou or so larger than the hole. This allows the chuck to be very accurately located and assures that it will not move around under load. Others feel that you should have some give in the hole and I happen to fall into this camp. I prefer to make the register a few thou smaller than the hole so I can indicate the chuck into near perfect alignment before locking it down with the locking bolts. Samchully, a maker of very high quality chucks, recommends this method and I've found it to work rather well.

Once you make the register/snout thing, you face out to flatten the remainder of the back plate and then mount the chuck. You then transfer the mounting hole locations that are already present in the chuck to the back plate with transfer punches and then drill and tap the back plate for your locking bolts. Then you bolt that sucker down and you have a new lathe chuck.

It is wise to mark each of the three pinions (a Sharpie works) and then insert a short piece of ground rod into the chuck and lock it down. Measure the run out of the rod with an indicator, then loosen the chuck and re-tighten with the next marked pinion. One of the three pinions will produce the least amount of run out. If you left some room in fitting the chuck to the plate, you can loosen the locking bolts to minimize run out and then lock it down for good. Re-check to be sure you know which is the most accurate pinion and then put a witness mark somewhere so you know which pinion it is. Also mark the spindle and back plate so you know the most accurate mounting orientation. When you remove and reinstall the chuck, align the marks. When you mount work in the chuck, use the marked pinion only and do not tighten the chuck with the other pinions. This will ensure that your chuck is as accurate as it can be.

There are videos galore on how to do this. Learning how to do this allows you to use any plain back chuck on your asian lathe so it is a skill well worth learning. There are many high quality chucks on ebay that you can buy for a song IF you know how to mount them.

EDIT: I highly recommend that when you find a source for your back plate and find that it fits your spindle well, buy at least two. If you mess one up, you have a back up. If you get the first one right, you have another for another chuck. If you ever buy another lathe, get one with a D1 camlock spindle. Almost every maker of high end chucks make them to fit a D1 spindle. It will likely be more accurate and it obviously saves you from the headache of mounting a chuck to a back plate.
 
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Creativechipper

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#15
Thanks guys, this info really helps!!

I never knew it was such a job to change chucks. Sounds fun
 
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