Wrong dial on lathe cross slide

SimonM

SimonM

Active Member
Since I got my lathe, I’ve been turning metal with no real purpose other than getting familiar with it. I could not get to the dimensions I wanted, regardless of the cut I was taking. Lack of experience I thought...

It always seemed off by the same factor. The dial is numbered 0-0.200” which I think should be diameter, not per side. After a while, i took out a magnetic back dial indicator to confirm the reading on the hand wheel and on the indicator I am getting 0.125” travel which doesn’t match what should be expected.

Turns out the lead screw is 8 TPI instead 10 which would match the dial. Compound is also 8 TPI but the dial is right. Everything seems original, must have been an Asian Monday morning 25 years ago...
 
YYCHM

YYCHM

(Craig)
Premium Member
Lead screw? Are you talking the cross slide screw and compound screw? What make and model lathe is this?
 
YYCHM

YYCHM

(Craig)
Premium Member
I recollect reading about this issue some where else..... Practical Machinist perhaps?

Now you have to wonder if the lead screw is compatible with the feed box. Have you tried threading yet?

Do you have the manual for the machine?
 
SimonM

SimonM

Active Member
I haven’t tried threading yet but I know what I’ll be doing tonight just for peace of mind.

I will also give the previous owner a call, he might know a bit more.

From my research, the Advance is Taiwanese and the house brand at Thomas skinner so I wouldn’t expect major issues.

I do have the manual, never thought about looking at it but there might have been different screws available.
 
Dabbler

Dabbler

ersatz engineer
The remedy is a bit time consuming but very easy. If you don't have a rotary table for your mill, someone else will, or you could borrow mine. You turn off all the markings on the dial, and remark it using your rotary table. When you have the additional bits, you can add the numbers to the dial as well, but it doesn't matter too much. Having the right meausrements is more important than the long spans...

You can take the opportunity to mark it as a .250 dial, which is then Diameter reading, instead of Radius reading, wich (in my opinion) is far superior...
 
SimonM

SimonM

Active Member
@YotaBota thanks for the link, my machine looks like the first one, just different colour.

@Dabbler no rotary table yet but it’s only a matter of time. My problem with borrowing tools is my geographic location (2 1/2 hours north of Vancouver) and not knowing any local machinists. Having the right measurements is important indeed. Using the dial indicator has worked in terms of precision but is only a temporary fix.
 
Janger

Janger

(John)
Administrator
Vendor
Create a new label for the dial on your computer with excel and the pie charting. print, laminate, glue in?
 
P

PeterT

Ultra Member
Premium Member
I cant get my head around why 8 TPI = 0.250"/rev. A finer pitch like 10 TPI is more suitable to smaller machine cross feed and 0-0.100" feed (0.200" diameter) mental math is simpler... at least for 10 fingered Neanderthals like me. You can get 10TPI rod & probably anti-backlash nuts, but now its the classic dilemma of needing a lathe to make parts for a lathe. And still left with re-scale the dials.
https://www.surpluscenter.com/Power...read-Lead-Screw-Nuts/ACME-Thread-Lead-Screws/

If its an otherwise decent machine that you intend to keep for a couple years, it might be worth investing in a 2-axis DRO. The Asian hobby systems are quite reasonable & reliable these days. That takes care of dial grads, backlash, zero set points, arguably accuracy & repeatability... You can then completely ignore the dial grads, or just use them for roughing.

Check your main lead screw pitch the same way you did the other axis just for completeness. Quite a few people experienced metric pitch in an IMP machine. They happily run the lathe power feeding for a few years, then graduate to threading time & then WTF.
 
SimonM

SimonM

Active Member
Tried my hand at threading last night and the result as were poor enough that I wouldn’t call it threads.
It’s only going to get better from here and that’s exciting.

I took a look at the manual and there were several dials and screws available.

@PeterT agree on the 8TPI, it’s not very intuitive.
 
H

historicalarms

Ultra Member
My "Taiwanese" 1340 lathe is the same as the OP's. Some manufacturer with a bunch of different name plate must have had the same bin of parts to assemble with.
My cross slide is marked the same "0-200 one mark=1 thou". I realized very soon that that wasn't the case , it is the same .00125 to each mark as yours is...didn't really concern me what thread the screw had at the time, it was just more of a "it is what it is" type of thing...but just remember that even tho your cross-slide movement is .00125 per mark, it does remove double that on a work piece dia. with every revolution so hitting a given thou with dial reading requires only a 1/2 mark movement.
 
SimonM

SimonM

Active Member
The dial is dual metric/imperial but none is right. It is bang on .125” and 8 tpi is a common thread that was offered.
 
P

PeterT

Ultra Member
Premium Member
That's what I was wondering too but an in-feed of 3mm would be another oddball dial graduation. For example 3/100 grad divisions = .03mm/line
A finer pitch lead screw like 2mm pitch would make more sense 2mm/100 grad=.02/division or 0.10 per 5 lines... something like that.
But he physically measured 0.125" so its highly likely an 8 TPI screw
 
Tom Kitta

Tom Kitta

Ultra Member
Could it be some custom thread? On BP style machines the set screws have a thread of 1/2-12 (if I remember correctly) not 1/2-13 and the 1/2-12 is US style not UK style.

Or they just installed wrong part or wrong parts were made in a large batch.
 
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