Confusing measurement

[Barking Mat]

Could it be the support to the dti is squiffy?

I'll go back to that corner and crack a beer, hmm nice corner, I'll be quiet.

 

[Barking Mat]

With a new straight bar in the chuck is the dti happy?

Stay in corner this time...

 

[My Old Landy]

I just watched the two Ox Tools videos, and at £35 for a bit of ally that size, I will leave my lathe to its own devices
Mine does have a little taper but it doesn't bother me. Once I have moved I may spent the time on it but it seems from the many posts on this thread, there are a lot of things that can influence it?
Edit: Just to say that my S&B has a cast head and the bed V's are full length. There is no adjustment there unless scaping in

 

[Screwdriver]

Could it be the support to the dti is squiffy?

I'll go back to that corner and crack a beer, hmm nice corner, I'll be quiet.

It could be ten thousand things. A loose floorboard, minor subsidence, mini earthquake but the idea is rather than guess, to try and analyse the situation from a position of status. What do we have on the spacecraft that's good.

Everything starts from a level bed, that stops the lathe from being twisted or bent and might even reveal on offset in the headstock. The headstock will be offset by any twist but it can also be adjusted. You obviously don't want to adjust the headstock on a twisted lathe or you can end up chasing your tail and finding that adjusting one thing has the opposite effect than intended.

In this case, it appears to be cutting a taper one way with off axis runout from the other. Sounds like a compound issue with the lathe tied in knots. There is only one way to be sure and that is to start from scratch.

 

[awemawson]

A/ Level the lathe to your best ability in X and Z making sure all feet are taking weight

B/ Check the headstock alignment using the Rollies Dad method previously cited

C/ Adjust Headstock (Colchesters have adjusting screw jacks between the ways), pivoting on the location dowel with hold down bolts just pinched

D/ REPEAT Rollies Dads method to prove that you've got it right (having tightened those bolts)

E/ Now adjust Tailstock to bring it into line using a test bar between centres.

F/ Sit down and have a few Old Speckled Hens

G/ It will now be bang on

 

[indy4x]

Yup like rocking horse poo

I had 2 with my M300, sold one and didn't make as much on eBay as I expected

 

[daedalusminos]

One thing I did discover from all this. A digital indicator can't be turned around like the clock type so it's upside down - progress eh

You bought the wrong model...

 

[fizzy]

I had 2 with my M300, sold one and didn't make as much on eBay as I expected

Typical

 

[fizzy]

You bought the wrong model...
View attachment 285742View attachment 285743

I had mine cheap though. Brand new but old stock and boxed. £50. Bargain I thought?

 

[Hood]

I have just taken a couple of pics to show the difference in bulk between the CNC and the Triumph.

Churchill Computurn CNC (base machine is a Polish Polamco TUR50 lathe)

Pic of across the ways.

Compared to the Triumph.

 

[fizzy]

Well I am an idiot!
I realised that the dti is below centre height. Didn't think it would make a difference.
But it does!. Doh
Now the dti measures the same across the bar.

 

[fizzy]

Just turned a very light cut with a very sharp tool. Then did a spring cut. Still 2 thou difference so not deflection. Just need to move the headstock 1 thou. Should be fun. Not today though will have to wait until Sunday.

 

[Pete.]

Just turned a very light cut with a very sharp tool. Then did a spring cut. Still 2 thou difference so not deflection. Just need to move the headstock 1 thou. Should be fun. Not today though will have to wait until Sunday.

Just make sure that when you take your measurement you put the DTI on the end furthest wawy from the chuck. If you move it 1 thou measured near the pivot (at the chuck end) the far end will move probably 10.

 

[fizzy]

Just make sure that when you take your measurement you put the DTI on the end furthest wawy from the chuck. If you move it 1 thou measured near the pivot (at the chuck end) the far end will move probably 10.

Yes will do!
I assume if it is 2 thou too big at the tailstock end then I move 1 thou towards the tool?

 

[fizzy]

A lot of Harrisons and Colchesters used a 4 ½ Morse taper in the headstock. They supplied a 4 ½ to 3 adaptor with the lathes, an item which usually got lost.

I think I found it earlier tucked away in the corner of the tool cupboard under the lathe!
Bit rusty so soaking in some Vinegar at the moment. Felt like Christmas finding that

 

[My Old Landy]

Yes will do!
I assume if it is 2 thou too big at the tailstock end then I move 1 thou towards the tool?

Do a sketch like Tom Lipton did in his video. That way you are tapping with confidence!

 

[Pete.]

Yes will do!
I assume if it is 2 thou too big at the tailstock end then I move 1 thou towards the tool?

Not exactly but it will get you close. The pivot on those is I think on the front left of the headstock so about 4" back from the front of the jaws and perhaps the same to the left. That means that the chuck end will swing about 1/3 to 1/2 as much as the far end

 

[fizzy]

I found the headstock bush as discussed .
Takes an MT4 but no idea what taper the outer is. Measures 2.25 one end and 2.12" the other. Length is 2.37" approx as measured with a vernier.