threading stop

This topic has 15 replies, 10 voices, and was last updated 23 July 2013 at 16:19 by capnahab.

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20 July 2013 at 16:41 #6789
capnahab
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@capnahab
threading sto
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20 July 2013 at 16:41 #125089
capnahab
Participant
@capnahab
Sorry about the rubbish picture. My lathe has a threading stop which stops the carriage advancing towards the headstock. The grub screw that locks it onto the bar has a thin disc of I think brass (3/16) that fits between it and the rod onto which it is supposed to clamp.

It has a habit of slipping if not done up extra tight. can anyone suggest a better arrangement. I wondered about adding another stop behind it.
20 July 2013 at 21:17 #125112
Grizzly bear
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@grizzlybear
Hi capn, Forget Moby Dick. More info required, if you would like some useful suggestions. Regards, Bear..
20 July 2013 at 22:18 #125116
Ian P
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@ianp
Totally agree more info needed.

How does it stop you threading?

Ian P
20 July 2013 at 22:54 #125122
capnahab
Participant
@capnahab
the arrowed sleeve with the grub screw visible slides on the rod so that you can fix it where you want the screw cutting to stop . grub screw is meant to lock it fixed on rod. carriage visible on right has a hole bored through it , rod passes through freely and carriage moves without touching rod. ( do let me know if I am not being clear ) . when screw cutting , carriage heads to left until it hits the stop , when it then pushes the whole rod the left and this disengages the feed to the leadscrew stopping the carriage.

its to stop you at the end of the screw cutting .

the problem is that the weight and momentum of the carriage is sometimes enough to push the stop so it slides on the rod risking the carriage not stopping where you want.

the grub does not contact the rod directly as it would swiftly wreck it. between it and the rod is a disc of brass 1mm thick by about 3 mm diameter which the grub screw pushes onto the bar. I think used presumably because to is softer and may conform better to the steel rod.
20 July 2013 at 23:06 #125123
Nobby
Participant
@nobby
Hi Capn

It may help if there was a flat on the bar so there is a larger area to clamp on with the grub screw with a flat on . or as you said back it up

Nobby
20 July 2013 at 23:15 #125124
1
Participant
@1
Without knowing anything at all about the machine under discussion, I think I would be looking at the force needed to push the stop rod towards the headstock and deactivate the carriage feed. Perhaps all that is needed is a little lubrication. I would have expected the screw and brass plug to fix the collar to the rod securely enough to operate correctly if it is a manufacturer designed arrangement.

Jim

Edited By Im Indoors. on 20/07/2013 23:16:44
20 July 2013 at 23:23 #125125
Michael Gilligan
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@michaelgilligan61133
Something that clamped onto the rod like a collet would be a very tidy substitute.

… but you would probably need two spanners to close it, instead of one Allen Key.

Thinks … Make it really well and perhaps two knurled rings would do instead of spanners!

.

MichaelG.

Edited By Michael Gilligan on 20/07/2013 23:24:27
20 July 2013 at 23:58 #125130
capnahab
Participant
@capnahab
thanks Nobby , good point , was wondering if there would be a softer alternative to brass or if I could make the brass disc curved to follow the rod.

thanks Michael , collet – now you're taking !.
21 July 2013 at 01:23 #125134
Andyf
Participant
@andyf
I'd forget the grubscrew. It, via the bit of brass, will only have line contact with the supporting rod.. Something which grabs the rod all the way round like a boa constrictor would get a better grip. Like the one in the middle of the top row in this picture.

Andy
21 July 2013 at 01:36 #125135
Ady1
Participant
@ady1
The simple answer is a beefier stop and a beefier bolt instead of a grubscrew

Bottom line is it's not up to the job and could damage your machine
21 July 2013 at 09:44 #125141
Sub Mandrel
Participant
@submandrel
I think Jim's point that the mechanisms may be stiff deserves some attention. Beefing up the stop may just be keeping you going until the day when the stop mechanism seizes and you have a big crash.

Neil
21 July 2013 at 10:15 #125144
Steamer1915
Participant
@steamer1915
That looks suspiciously like a Hardinge machine to me. I would agree with Neil, as I have never had an issue with the stop moving on mine and I have screwcut up to a shoulder at 1000 rpm, leaving about 5 thou to spare. I would suggest that you investigate why the rod is so stiff to move. Does the handle feel stiff when you knock it across to either cut the thread or on its return journey? I would have to disagree with Ady1 – it is up to the job – something else is amiss. Fix the problem not the symptom.

Steve.

Edited By Steamer1915 on 21/07/2013 10:15:54
21 July 2013 at 10:41 #125149
capnahab
Participant
@capnahab
It is a hardinge and Yes , the handle does feel stiff , in both directions … Good diagnosis Steve. Have you had similar ?.
21 July 2013 at 10:47 #125150
Steamer1915
Participant
@steamer1915
I have never had a problem with either my own or the one that I used in my former place of employment. I can only suggest following Jim's advice and try to lubricate all points of the linkage etc. Sorry, but I have never had this part of the machine to pieces.

Steve.
23 July 2013 at 16:19 #125312
capnahab
Participant
@capnahab
Thanks Graham, I also work for the Nhs and for various reasons I cannot get at the machine to check details.However, I have checked the grub screw and copper ( think mines brass) and all is fine . I think its a stiff selector lever that's the problem. I have only recently got the machine. The selector lever is stiff on moving into forward or back largely. I have the Babin attachment for threading (http://m.youtube.com/watch?v=wewJ_LI54W4 which bypasses the box using a servo on the leadscrew controlled by a dedicated microprocessor.

I need to check the rod at both ends and the 3/4 nut and spring washer on the back of the lever.
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