Mounting a new chuck on lathe

[Mark BParticipant @markb43031]

[Mark BParticipant @markb43031]

I want to mount a new chuck onto my Lorch lathe instrument makers. The headstock spindle has a 20mm x 2.5 metric thread.

I am planning on getting an unmachined backplate from Chronos like this:

https://www.chronos.ltd.uk/cgi-bin/sh000001.pl?WD=backplate&PN=Unmachined_Chuck_Backplates%2ehtml#a112175

My question is around the cutting of the internal thread on the backplate. Would I get acceptable results from using a tap like this or should be thread be machine cut on a screw cutting lathe?

https://www.tracytools.com/taps-and-dies/metric-taps-dies/20-x-25-metric

I'm hoping the tap solution will work.

Also should I invest a little more in the HSS version of the tap?

 

Edited By Mark B on 31/01/2019 13:16:21

Edited By Mark B on 31/01/2019 13:16:45

[Speedy Builder5Participant @speedybuilder5]

I suspect the lathe's spindle nose has a collar which the back plate butts up against, so it is essential that the thread of the backplate is as near as possible perpendicular to the mating face on the backplate. Screw cutting would be the preferred method as this will give the desired result. If you use a tap, it may wander out of perpendicular to that face.

The second part of good repeatable alignment is achieved by the bore of the backplate locating on the un-threaded portion of the spindle nose adjacent to the spindle nose collar.

BobH

Edited By Speedy Builder5 on 31/01/2019 13:30:36

[Michael GilliganParticipant @michaelgilligan61133]

Could you post a photo of the spindle nose please, Mark

If it has a 'register' then a tapped thread should do fine … because the register does the accurate bit.

But if it relies on the thread, then screwcutting would be preferable.

MichaelG.

.

Edit: Bob beat me to it.

Edited By Michael Gilligan on 31/01/2019 13:31:51

[Mark BParticipant @markb43031]

Thanks for responses.

I'll have to take a better picture when I'm home from work, but this gives you an idea. I'm pretty sure that the existing chuck I have butts up to a register.

**LINK**

Better picture to follow.

[Michael GilliganParticipant @michaelgilligan61133]

That looks fine, Mark

The precision of registration should be provided by that long parallel section, and the screw-thread in the backplate will effectively just be a 'nut'

Get the plain boring right, and tap the thread [with due care and attention of course]

MichaelG.

.

Edited By Michael Gilligan on 31/01/2019 14:51:22

[Mark BParticipant @markb43031]

Thanks for the reply – that's really helpful.

In terms of purchasing taps is there a big benefit to getting a HSS one for cutting the casting material or will a standard one do. I'm not planning on doing this operation lots of times…  the HSS tap costs x3 as much.

Edited By Mark B on 31/01/2019 17:19:49

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Mark B on 31/01/2019 17:19:14:

In terms of purchasing taps is there a big benefit to getting a HSS one for cutting the casting material or will a standard one do. I'm not planning on doing this operation lots of times… the HSS tap costs x3 as much.

.

I think the 'carbon steel' version should be adequate for what you're doing, Mark.

Incidentally; does the chuck in the background of your photo fit the Lorch nicely ? … If so, I suggest you briefly remove it from the backplate and have a look at the 'fit' of the plate to the spindle nose; to give you a better feel for what you need to do.

Please do keep us informed.

MichaelG.

[Author]

Posts