AL320 Screwcuting Problem - Help!

[Bidgee]

Need some direction on getting this one sorted.

Bought this lathe 2nd hand in v good nick. Messed around learning to use it and cutting a few threads etc. Was having no issues but now when I tried to cut a thread again the other day the tool will not track exactly back over the last cut using the chasing dial and half nut.

If I use the fwd/rev switch on the motor I have no issues but Im sure this is not great for the motor.

Any ideas where the problem might be?

Thanks

Scott

[Dave J]

With out more info on thread etc, but if your cutting a metric thread on an imperial lathe or a imperial thread on a metric lathe you can not disengage the half nuts. You need to reverse the motor to back, and go passed where you started before taking another cut to take up the backlash.
Hope that helps.
Dave

[Bidgee]

With out more info on thread etc, but if your cutting a metric thread on an imperial lathe or a imperial thread on a metric lathe you can not disengage the half nuts. You need to reverse the motor to back, and go passed where you started before taking another cut to take up the backlash.
Hope that helps.
Dave

Thanks Dave

I was cutting 1.25 and 1.75 metric threads on a metric lathe.

[Dave J]

Metric lathes come with a few gears for the thread dial, you need to select the right gear to suit the thread your doing.
Dave

[Bidgee]

Not this one. The chasing dial gear is pinned.

The pitch of the cut is correct so no problem there. The issue is the tool can be out by half a thread next cut.

This is the machine https://www.machineryhouse.com.au/Products?stockCode=L141

[Dave J]

Hi,
What does the instruction book say about the tread dial. I have an imperial lead screw lathe so I am not 100% sure. I thought they all had a few gears like this one in the link.
Chester UK Ltd :: View topic - Crusader screwcutting drop in dial (http://www.atfreeforum.com/chesteruk/viewtopic.php?t=383&mforum=chesteruk)
Dave

[Bidgee]

Its Chinese so instructional info is very sparse. It doesnt mention changing anything on the chasing dial and it cannot be adjusted like in the link you provided.

[Dave J]

That fellow modified the one in the link. When he got it, it only took one gear which he said was a pain so he made an adjustable mount and put all 3 gears on the shaft.
Yours has got me stumped, I don't know to much about the metric lead scews other than them having the few gears for the thread dial. I know a few people on here have the same lathe maybe they will help out.For now you will just have to back it up. It wont hurt anything as long as you let the motor stop. I have to do this when cutting metric threads.
Dave

[bollie7]

If you haven't already tried this, try engaging the clasp nut and then marking the chasing dial so that you only engage on the same mark every time.
The only other thing I can suggest is have a look and make sure that there is nothing loose or wrong wih the clasp nut assembly.

regards
bollie7

[Dave J]

I have been thinking it over. Is there a chart for the thread dial on the carriage or the head stock? I know mine has but it's imperial. On mine for some threads you have to drop it in on different numbers.
Dave

[Bidgee]

I have been thinking it over. Is there a chart for the thread dial on the carriage or the head stock? I know mine has but it's imperial. On mine for some threads you have to drop it in on different numbers.
Dave

No the only table is for the thread cutting gear changes. This has got me stumped too.

I have checked the pitch of the lead screw and its 3mm (10 turns of the lead screw moves the carriage fwd 30mm). I assume this makes it metric. I wanted to check as I thought maybe the lead screw had been replaced with an imperial one.

Bollie, good idea. Given that it cuts OK as long as the half nut is not disengaged maybe the issue is in the half nut engagement assembly.

Thanks for all the suggestions.

Scott

[Dave J]

Re reading your post and seeing you were having no trouble before, I am thinking :?it might be the shear pin in the lead screw near the head stock. With the lathe off try gripping the lead screw (with something around it to protect it) and try turning it to see if it turns with out the gear box.
Dave

[Bidgee]

I can see the pin and its OK.

[Dave J]

Some times when they brake they look just the same because they shear inside, just a thought.
Dave

[Bidgee]

Dave, I think I've narrowed it down. When I engage the half nuts there is some play in the carriage wheel. If keep fwd pressure on the wheel the tool tracks the last pass. If I take the pressure off it lags half a thread.

Looks like I need to pull it to bits and see what's going on.

Appreciate all the help.

Scott

[Dave J]

On mine there are 2 small allen key bolts with nuts on the left hand side of the carriage to adjust sideways movement of the half nuts.
Dave

[pipeclay]

When you engage your half nuts how far past the end of your work piece is the tool.

From what you mentioned about the carriage hand wheel it maybe backlash.

[Bidgee]

When you engage your half nuts how far past the end of your work piece is the tool.

From what you mentioned about the carriage hand wheel it maybe backlash.

About .25" past end of work.

[pipeclay]

Try running the tool a bit further past the end,to see if it tracks the thread any better,mayb an 1" or so.

[Dave J]

Sometimes it takes a turn or 2 of the lead screw to take up the backlash.
The hand wheel runs off a rack under the ways, so if you say it works holding onto it, it does sound like backlash.
Dave