Is it ok to mount a 4 inch chuck on a MT3 Morse taper?

J

Joez71

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My little lathe has a fixed 4 inch 3 hole backplate, I have a 4 inch 4 jaw chuck I want to use but it has 4 holes not 3.

I was going to make an adapter as I am struggling to find anything here in Australia that will work. That will go from the 3 to 4 hole layout but I was looking at the bore on the lathe and I realised its an MT3.

Is it a bad practice to mount a chuck on a MT3? If not is there a morse taper that will fit the bore of the chuck. I quickly measured it and its 22mm .8661 inches.

Sorry if my terminology is wrong... Hopefully, I am making sense.


PS if anyone knows of a suitable adapter I'd also be interested as long as shipping isn't prohibitive.



Thanks
joez71
 
A picture would help here because I don't see the problem.

Sounds like you need an intermediate round disk with a hole in the center to give access to the bore. It needs 7 holes. 3 to hold the disk to the backplate on the lathe and 4 to hold the chuck to the intermediate disk.

I gather your spindle bore has an MT3 taper but don't see why that's needed to mount an intermediate plate and chuck.

Ray
 
You need to try an MT3 taper in the spindle to confirm it is MT3, not just the opening diameter.

As Ray said, a backing plate may be easier with 7 holes.

If you do use MT3 taper on a chuck, you need to use a drawbar to keep the chuck in place to prevent vibrating loose. You also loose through hole capability, only as deep as the chuck.
 
Personally, I would go with the disk for reasons given above.
Mount a piece of plate roughed out to the disk shape to your back plate. Face the plate to true it up and flip and face the opposite side and turn to diameter. Add any registration features that may be required for the 4 jaw, mark out a bolt circle for drilling and tapping your chuck mounting holes. Use the chuck as a guide for locating the holes.
I would use something like 12-15mm plate for the disk. I would counterbore the mounting holes to your backing plate to permit facing. If the plate is thick enough, you will be OK with counterbores on each side. If the four holes in your chuck are tapped, you will have to rethink the process as it isn't possible to mount the disk to the back plate when it is mounted to the chuck. You would have to drill through holes in the chuck and use bolts. I would counterbore or countersink the holes so the bolt heads would be below the surface of the chuck face.
 
Are you sure you can't remove the backplate? That would be the normal thing to do. That's how all of my lathes have worked.

As Dave Paine said, you'd probably need to use a draw bar to hold onto the chuck. Both of my lathes have an MT3 taper in the head stock. I use an MT3 to MT2 adapter to hold my collets. The MT2 collets are inexpensive and easy to find. It wouldn't hurt to have collets available for your lathe.

These are examples, not recommendations. You can probably better research this on your own for Australia.

https://www.ebay.com/itm/MT3-to-MT2...eeve-3MT-to-2MT-in-Prime-Quality/331859218832

https://www.ebay.com/itm/7-Pc-2MT-R...Pc-Set-1-8-1-2-MT2-3-16-1-4-3-8-/112343332131

Mr. Pete's video on the subject:

 
Joez71 said:
My little lathe has a fixed 4 inch 3 hole backplate, I have a 4 inch 4 jaw chuck I want to use but it has 4 holes not 3.

I was going to make an adapter as I am struggling to find anything here in Australia that will work. That will go from the 3 to 4 hole layout but I was looking at the bore on the lathe and I realised its an MT3.

Is it a bad practice to mount a chuck on a MT3? If not is there a morse taper that will fit the bore of the chuck. I quickly measured it and its 22mm .8661 inches.

Sorry if my terminology is wrong... Hopefully, I am making sense.

PS if anyone knows of a suitable adapter I'd also be interested as long as shipping isn't prohibitive.

Thanks
joez71
Click to expand...

G'day Joez71

welcome to this great forum we are here to help. Firstly a few questions what brand and model is your lathe.

Pictures always help when asking questions.

I very strongly suggest that you follow the mounting set up that is already on your lathe. Using an MT3 or any other size is fraught with danger. MT spindles have a reputation for working loose unless under compression load at all times, so at the very least you would need a draw bar, but you would also loose the through hole, which is very handy, very often.

So back to the backing plate, can the backing plate be removed? If so redrill it to suit the new chuck. If not you can either drill the chuck to suit the backing plate, or make an intermediate plate to adapt between the existing plate and the new chuck.

You're lucky in Melbourne you have the choice of a large number of machine tool shops surely one of them can supply a ready made adaptor plate for your set up. Who sells your lathe new in Melbourne.
 
Do you have a flanged or threaded spindle nose?
Mark
 
Thanks, everyone for the feedback.

I have sourced some material for a suitable adapter. Didn't think taking the MT3 route was a good idea, sounds like I was right.

I've attached a couple of pictures of the lathe in question, its not new, probably about 10 years old but unused. I've had a couple of other people with the same lathe tell me the backplate is fixed, strange arrangement IMO.

joez71
IMG_8001.jpgIMG_8002.jpgIMG_7996.jpgIMG_7999.jpgIMG_7998.jpgIMG_7997.jpg

IMG_8001.jpg
 
OK... Yes, you just need an intermediate disk. If you're not planning to take it on and off frequently, an aluminum disk will do just fine. Here's a sketch of what you need. Notice 4 holes are counter-sunk so the heads of the bolts are below the surface of adapter plate. Three of the holes will need to be threaded. You may need to purchase new bolts of the proper length.

ChuckAdapter.JPG

Ray
 
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