Lathe Screw info plz

[Piero]

Hi Guys

Trying to identify this acme screw

It has a dia of 15mm and has 10 tpi

the thread length is 19 cm and overall length is 41 cm

I believe it could be (not certon) a Colchester chipmaster crosslide screw in metric

 

[Pete.]

Certainly looks like a colchester cross slide screw bit if it was metric it would be 2.5mm lead not 10tpi ( which are very hard to tell apart, you have to measure over 20 pitches).

It should be a twin-start thread if it is.

 

[Piero]

Pete

whats a twin start thread???

Tried emailing Colchester lathes,

got a reply saying its a Bantam, !!!!!

I told them the part number on the package was 2155, and I also told them I had no way of saying if the package and part number was correct for the part.

they reply was it looks like a bantam screw of part number 2155.

ONLY on my parts listing, 2155 is from a Chipmaster!!!!!

VERY confused now

 

[Seadog]

A twin start thread is exactly what it sounds like Piero. If you look at the end of the thread you will see that there are two threads running side-by-side. The starts of each are at 180 degrees to each other. You can get three, four or more start threads.

 

[Piero]

I thought it was, but wanted to be sure, so I asked.

This is a single start thread

why would a metric thread need to be twin start ????

 

[Seadog]

It's not down to the thread standard. A double start thread advances twice the distance for the pitch that a single start one does, a three start three times the pitch etc. Often used in tailstocks, the Myford being one that springs to mind.

 

[Piero]

maybe I am missing something here

Pete said it should be a twin thread screw,
he was not clear if he was saying that for a metric, or imperial thread or both.

I cant see why you would have a twin thread for one (lets say metric) and not the other (say imperial)

 

[I'm getting on a bit]

maybe I am missing something here

Pete said it should be a twin thread screw,
he was not clear if he was saying that for a metric, or imperial thread or both.

I cant see why you would have a twin thread for one (lets say metric) and not the other (say imperial)

Think of it this way

A 5mm single start would give 5mm cut per rev or 10mm off the diameter

You would double that for twin start

Theoretically the bigger the movement the less accurate

As say a cylindrical grinder would remove approx 1mm per rev and the handwheel would be approx 200mm diameter

 

[Piero]

I get what a twin thread does.

What I don't get is why only a metric thread would be twin start and not the imperial as well (as was suggested earlier )

 

[I'm getting on a bit]

Maybe Pete is mistaken as 10mm per rev does seem excessive

 

[Piero]

the screw in question has ten threads in one inch of length

 

[MBB]

Chipmaster 2start left hand thread earlier ones had a single start thread

 

[Piero]

Interesting

The part number does suggest it to be chipmaster.

But like I said. It was in a opened packing.

The packing might not have come from this screw

 

[MBB]

Is it for sale?

 

[Pete.]

The Bantam imperial cross-slide screw is a two-start thread having .100" (10tpi) pitch and .200" (5tpi) lead. The important bit is the lead, that's what sets the movement per turns of the dial. Since the dial has 200 graduations it's a 5tpi leadscrew.

I believe the Chipmaster and Bantam share the same parts for the cross-slide so that might explain the part number thing.

BTW I can make these 2-start screws if anyone needs them. Apparently it's common to graft a new screw section onto the front of the cross-slide though the spline wouldn't be too much trouble to make either.

 

[Pete.]

Is it for sale?

If it is, I would love to get hold of it to take some measurements. It's rare to find a new genuine one and they are uber-expensive from 600 group.

 

[Piero]

Now being at my workshop today.
I have ruled out the packaging and part number to not belong to this crosslide screw.

This is a imperial thread.

I am thinking it's from a mk1 bantam English lathe

Does any one have a photo of such a crosslide screw

 

[Pete.]

Don't you have a mk1 Bantam yourself Piero?

 

[Piero]

I do indeed.

And it's imperial whoop whoop.

I manged to bag two of these crosslide screws. One new still in its wax coating and the other nearly new with very very light use.

The packing was miss leading.

I have had two emails from Colchester lathes here in the uk.

They seem to believe the bantam and chipmaster both share the same crosslide screw.

I'd be very interested if someone else could confirm the chipmaster conection as these screws also came as two complete sets.

Two crosslides. Two compounds two tailstock.

The crosslides and compounds look the same as my bantam but the tailstocks look more like the chipmaster.

So with that said. These sets look to have come from a chipmaster but the crosslide and compounds could be interchangeable with the bantam.

If anyone can confirm this that would be smashing

 

[Dieselman 63]

@Maker has a Chippie

I have some questions regarding the Mk1 Bantam gearbox and apron which I have been unable to solve on my own, if you have stripped your machine and rebuilt it?