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old hack
05-16-2007, 05:34 AM
I would like to have a go at screwwcutting on my new Hafco lathe,
Problem is my lathe doesnt have a chaser dial or a brake

although i did see on a site somewhere recently where someone had fitted an indexed wheel to the tailstock end of the leadscrew.

would that serve the same purpose ??

JCHannum
05-16-2007, 05:44 AM
In short, no. The threading dial indicates the position of the cariage in relation to the leadscrew. An indexed wheel on the leadscrew is used to indicate distance moved.

oldtiffie
05-16-2007, 06:16 AM
Deleted/edited-out

Your Old Dog
05-16-2007, 06:25 AM
I took a tip from Evan here on the forum and made a hand crank setup for my lathe as i was having trouble threading too. It works fine, slows things down so you don't have to worry about mangling up the machinery!

I just made an expanding collett for the other end of the quill and put a hand crank on it. (might be a good idea to pull the power plug if you're as absent minded as I ! )

dp
05-16-2007, 12:14 PM
My lathe has neither a brake nor a dial. I am making a dial but got gave it a lowere priority when I realized I could thread just fine without it. For threading to a shoulder I made a handwheel that allows me to manually turn the lathe with the half-nuts engaged to the lead screw.

The only convenience I have is my lathe motor is reversible so I can leave the half-nuts engaged and quickly return to the beginning of the cut (with the cross feed backed out, of course).

R W
05-16-2007, 06:40 PM
Page 82 in "Running An ENGINE LATHE" by Fred H Colvin, describes a method
for engaging the half-nuts at the correct time on lathes not fitted with a threading dial.I have not tried it.

Carl
05-16-2007, 09:42 PM
There are several ways to do it without a threading dial. Easiest is stopping the lathe at the end of the thread, retract the tool, reverse the lathe back to the start of the thread, return the cross slide to it's original setting, advance the tool with the compound, and start the lathe in forward motion again.

Mike W:

I have not tried it but I heard that a mark on the chuck and one on the leadscrew can be used to indicate when to engage the halfnuts.
Mike W is right, except you must also have a positive stop to bring the carriage back against...usually the tailstock set against the carriage.

You can also stop the lathe at the end of the thread...retract the tool...mark the ways at a fixed point on the back edge of the carriage...measure off and mark exact half inch intervals for an even thread...or exact one inch intervals for an odd thread...disengage the halfnuts...run the carriage back to the start of the thread stopping on an appropriate interval line...re-engage the half nuts and restart the lathe after making the appropriate tool adjustments.

The index wheel on the end of the leadscrew will not work because a threading dial shows the relationship between the carriage and the leadscrew...and an index wheel on the end of the leadscrew has no relationship at all with the carriage.

kap pullen
05-17-2007, 07:03 AM
Quote Carl;


"...You can also stop the lathe at the end of the thread...retract the tool...mark the ways at a fixed point on the back edge of the carriage...measure off and mark exact half inch intervals for an even thread...or exact one inch intervals for an odd thread...disengage the halfnuts...run the carriage back to the start of the thread stopping on an appropriate interval line...re-engage the half nuts and restart the lathe after making the appropriate tool adjustments...."


Carl,

The spindle also has to be reset (rotated), and started at the same angular position does it not?

A metric lead screw won't pick up on half inch spacings.

A lathe will pick up at the same carriage/spindle location each time on the appropiate threads (inch or metric).

Kap

oldtiffie
05-17-2007, 10:59 PM
Marv Klotz has addressed this very problem with his "stick" utility on his web page at: http://www.myvirtualnetwork.com/mklotz/

He has simplified the problem beautifully and addresses the perennial problem of "metric threads on and inch lead-screw" and vice-versa. He has "pulled all the threads together" and explains how it works and why he did it.

QED

But in downloading it, DO read and understand the process as it will simplify it to the extent that you will "know what you are doing" instead of just "doing as you are told".

Marv Klotz also addresses the setting up and use of the lathe top slide for screw-cutting as well.

And they run under the Windows DOS-emulating "command" function.

I'd also suggest that you have a look at a beautifully "simple to use and simple to make" tool and software for grinding the screwing tool correcly. It is at: http://davidh.idx.com.au/paget.html

Also, you might like to check out suggested lathe tool angles at: http://shopswarf.orcon.net.nz/turntool.html and while you are there, take my advice and check out the "index" at that site as well as it has some nice surprises.

And here endeth the lesson.

(and who the bl**dy hell said "Amen - and about time too?")

BillB
05-18-2007, 09:18 PM
Keep in mind that if you can find a used threading dial from another brand of lathe with the same pitch & diameter lead screw, it can easily be adapted. I think the dial on my SBL was made by Clausing.

BillB

franco
05-18-2007, 09:48 PM
BillB,

According to Hafco's website:
http://www.hareandforbes.com.au/sample_2/home.php
the AL320 has a metric leadscrew. This limits the options a bit for using a thread dial from something like a South Bend. For cutting metric threads with a metric leadscrew, there are usually several gear wheels (often four) on the thread dial indicator which mesh with the lead screw. Each one will cover a range of metric pitches, but all of them are needed to cover the whole metric range.

franco