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Lathe crash!

Screw cutting disaster :(

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Andrew Johnston01/01/2019 16:31:17
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This thread suggests an alternative, essentially moving both the saddle and spindle back to the original starting point and relative orientation:

**LINK**

As background I have now used the Ainjest unit for many screwcutting jobs. I normally allow 4 thou clearance for the trip both internal and external. Thus far I've only cut imperial threads (on an imperial lathe) with the unit, but as and when I need to cut a metric thread I'll investigate the method in the link above.

Andrew

Ian Skeldon 201/01/2019 17:09:46
366 forum posts
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ChrisB I had a nightmare getting my lathe to cut the thread I wanted (internal and external imperial on my metric lathe).

Thankfully there was an answer and pretty much all of those involved in this thread helped me to sort it out, looks like your issue is going to be more difficult to resolve, maybe buy a load of bushes and hope you never need them wink

Ian

Chris Trice01/01/2019 18:27:23
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Posted by JasonB on 01/01/2019 16:29:01:

No Clutch, I think Chris was asking about a motor to spindle clutch not a screwcutting clutch

 

Correct. Sorry if that wasn't clear. What about a retracting cutting tool or one that swings up out of the way? Good for external threads but no good for internal. 

 

 

Edited By Chris Trice on 01/01/2019 18:28:39

Michael Gilligan01/01/2019 19:03:08
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Posted by Chris Trice on 01/01/2019 18:27:23:
 
What about a retracting cutting tool or one that swings up out of the way?

.

Such as designed by the aforementioned Martin Cleeve:

[quoting from a recent thread]

Here is the design for the one I like: **LINK**

https://archive.org/stream/PopularMechanics1976/Popular%20Mechanics-04-1976#page/n105/mode/2up

MichaelG.

.

Ref. Christmas Eve

https://www.model-engineer.co.uk/forums/postings.asp?th=139739&p=2

 

Edited By Michael Gilligan on 01/01/2019 19:05:19

ChrisB01/01/2019 22:02:37
294 forum posts
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Posted by JasonB on 01/01/2019 16:29:01:

I tend to cut away from the chuck at the back so don't have to worry about stopping in a rush if going to a shoulder and can cut faster so can stop easily and run in other direction to take me back to the start.

Would that mean inverting the tool upside down like in this video ? **LINK**

 

Posted by Chris Trice on 01/01/2019 18:27:23:
 
What about a retracting cutting tool or one that swings up out of the way?

Good idea Chris/Michael, would make a nice project - I just need time, sometimes I wish a day was 48hrs!

 

Posted by Ian Skeldon 2 on 01/01/2019 17:09:46:
 
maybe buy a load of bushes and hope you never need them

Should not need any bushes anymore if my planned mod works out...but I'll keep a couple of spare keys just in casesmile p

 

Bushes and keys - the key is aluminium so there's an easy fix failsafe should I mash up again. Bushes are 8mm dia instead of the original 10mm - not sure of the material, could be stainless or titanium as I mage them from a bolt which conveniently was the exact outside diameter.

1d.jpeg

Conveniently used a 5/16" cres bolt which fits perfectly on the 8mm bushes. Added a grease point for lubrication and rethreaded the bolt to M6 to fit the T-nut on the banjo.

1b.jpeg

Bushes are a sliding fit on all gears, so there'e no more tapping to force them on. As the gear bores are not exactly uniform some fit a bit tight while some slide right on but none are loose or hammer tight.

1c.jpeg

The gears will slide right off the shaft when the retaining washer is removed ( it will either be a c-clip or two halves) so I won't need to take the whole thing apart.

1a.jpeg

Will see how this works, and maybe post a video if it runs ok.

Edited By ChrisB on 01/01/2019 22:04:49

Michael Gilligan01/01/2019 22:53:50
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Looking good, Chris

MichaelG.

ChrisB09/01/2019 21:16:26
294 forum posts
122 photos

Tried and tested the new bushes this week and found some time to take video. It's working fine till now. Cut some M16x2 threads and changed back gears for normal turning with auto feed.

Now time will be the real tester!

ChrisB11/01/2019 16:32:08
294 forum posts
122 photos

Posted by JasonB on 31/12/2018 20:32:52:

But the whole reason Chris had a crash was because he did not want to disengage the nuts, what use is a system to disengage them, he could have just flipped the lever and drilled his hole if he could disengage them.

I'm assuming the Meek clutch will mean you loose your position when cutting say metric threads on a machine with imperial leadscrew.

Regarding thread cutting metric threads on imperial lathes, I cannot disengage the half nuts otherwise I'd loose my position - I have noticed that I can switch the feed direction knob with the lathe running at the lowest speed without any rattling of the gears (at 3:18 in the above vid clip I'm switching directions)

Has anyone tried this before, and is it recommended? I'm tempted to give it a try on my next thread cutting project.

Journeyman11/01/2019 16:50:16
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ChrisB, I would have thought that going directly from forward to reverse is likely to impose an undue strain on the electronics. Better to stop in between, also you still need to retract the tool before going into reverse so some frantic handle winding at the same time as flipping the reverse switch, an exercise in co-ordination frown

(On another matter, I note from your video above that you wear a ring. NOT a good idea in the workshop always told not to during my training days and shown the gory pics to go with the advice!)

John

Edited By Journeyman on 11/01/2019 16:57:47

ChrisB11/01/2019 17:26:14
294 forum posts
122 photos

I guess that would be correct if I flipped the electric direction change over switch on the top control panel. I'm referring to the feed direction selector knob (which is mechanical) on the lower part of the headstock. The direction of rotation of the motor and chuck remains the same, what changes is the direction of movement of the carriage. So let's say I'm cutting a LH thread - I turn the feed selector to the left and start cutting, when the cutter is up to the shoulder I switch the feed selector to the middle position and the feed stops, I can then retract the tool and switch the feed selector to the right, and repeat the process...don't know if I'm explaining myself properly.

You're right about the ring John, thanks for pointing that out...have to make a habit of taking that off

Edited By ChrisB on 11/01/2019 17:26:58

Journeyman11/01/2019 17:36:09
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ChrisB, must admit I've never tried that on my WM250. But when stationary the feed change knob always seems to be clunky and sticky always have to check that it is not still in neutral. Having had the gearbox cover off the gears are fairly crude but if it works why not. I can recommend a flip-up tool holder when screw-cutting.

John

Bazyle11/01/2019 17:36:13
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Using the 'tumbler reverse' will lose your registration of the spindle and leadscrew because it is changing some gears around.

JasonB11/01/2019 18:20:59
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It has no tumbler but I think the effect of using the front gearbox will be the same, Will look into it a bit later and get back to you, need to find my photo of whats inside as it is a while since I opened mine up.

If I want to cut on the back stroke I tend to go from fwd, pause in neutral and then into reverse which seems kinder to the lathe

Edited By JasonB on 11/01/2019 18:21:10

ChrisB13/01/2019 16:57:39
294 forum posts
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As Bazyle predicted, it does not work this way. I tired cutting a test thread to see if the next pass aligns to the first pass after disengaging through the feed selector knob - it does not align at all, it's similar to disengaging the half nuts...

I have something else in mind which might work, something which Andrew Johnston pointed out in a post above, about moving to the exact position original starting point...

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