Threading

Evening all.

Had the day free so I have been dabling in a bit of thread cutting. I need a back plate for my four jaw in 7/8x12 tpi (myford 3 1/8'' so have been messing around with that thread. What would be the best method for getting to start on a (stone age) manual machine? I mean in terms of acurate setting. In my messing I used a clamp as a stop but it moves easily on reversing up to. I was thinking a carrige stop style clamp with a DTI attached alowing measurement would be better? Last piece of the puzzle guys.

Cheers.

David.

Hi David, not sure what you want to know ???

Regarding the thread cutting, do you have a chasing dial? have you worked out he change gears? Are you wanting to know how to set the tool to thread depth? or is it how to pick up the thread for successive cuts?

Looking at you photo's I assume its for the lathe shown thus no chasing dial?

Where are you located ?

Hi David
Looking at the photos . I cant see any change wheels/gears or studs . Has it got a back gear you can engage for screwcutting I cant see a thread indicator .As John said we need more info.

Nobby.

Evening guys.

Sorry a bit vague I'm from cardiff. I was having trouble, i.e parting the thread but managed to suss it. Mounted a dial indicator to the bed but its on its way out, which was why I was getting parts. No thread indicator sorry. I am using back gear for cutting, naturally. Its a slow process without tumble reverse though as you can imagine guys! Couple of pictures of my set up.

Is this the best way to go about the task. Its the best I can think of. I set up the gears using that NPprogramme. Not getting the TPI I would like think its a miss understanding of idler gears. I'll take another pic of my banjo setup.

Cheers for the input guys much appreciated.

David.

Edited By woody1 on 04/03/2013 23:18:34

Edited By woody1 on 04/03/2013 23:40:20

Edited By woody1 on 04/03/2013 23:42:55

Hi David,
I'm don't fully understand your question. I do not understand what the stop is for.
My understanding is that you are trying to cut a female 7/8" x 12 TPI thread in the backplate for your 4 jaw chuck. I assume you will mount the backplate on a faceplate. To check the thread when you get near to finished depth you will need to unscrew the faceplate from the spindle so you can try your new thread on the spindle.. I would suggest marking the alignment of the spindle and faceplate so you tighten it back to the same position so you do not have any misalignment between the tool when you take the next cut. If you give information about the pitch of your leadscrew and the number of teeth on the gears you plan to use (Including the number of teeth on the spindle gear.) we will be able to tell you if you can disengage the half nut without loosing position, If not you will have to wind the lathe backwards.
For such a short thread (Probably less than an inch.) I would turn the lathe by hand. While thinking about this (1" of thread at 12 TPI would be 12 turns.) it made me wonder if 12 TPI is correct. I would have thought the spindle thread to be shorter.

Les.

Hi David
I cant see them have you micrometer dials on the lathe ? I see you have the compound on an angle ?
as Les says you could use one of these and leave the half nut closed Nobby

Nobby

David,

To add to the advice already given, it is always helpful in such a case to prepare in advance a dummy of the lathe spindle nose; you can then use this to check the progress of the female thread. It is a lot easier to cut an accurate male thread than the female equivalent, and having the dummy will avoid the need to take the backplate off to test it, with all the risks of misalignment when returning it to the lathe.

I'm not familiar with the lathe this is for; if it has a parallel portion at the bearing end (as the 7 series does) then cut this first - on the outside, of course, on your backplate.

David

Edited By David Littlewood on 05/03/2013 15:46:26

Afternoon guys.

No dials im afraid on the controls but two DTIs, one on the cross slide to reset zero after a pass and one mounted on the bed to get back to start point zero i was originally using a g clamp and winding back to set zero. I leave my half nut closed just dis-engage back gear after completing a pass and wind backwards using lead screw handle slightly past zero then forward to zero because of backlash. my four jaw backplate is of the wrong size, luckily its smaller so I only need to bore it out and re-thread. Can I use the three jaw for the operaation? For now I am concetrating on external threading my plan is to make a replica of my spindle nose. then move to internal.

Excuse the rust first time out for the gears. The programme states for 12 tpi 45 driven which is on the lead screw and driver 30 which is on the manderal. the other two are idlers? I think this is wrong though. I have read the spindle nose could be 12tpi but also read it could be 8 tpi? I do know how ever my lead screw is 8 tpi. looking at the picture I can see I have the 30 on the leadscrew and the 45 on the manderal doh!

Again thank for your time guys.

Edited By woody1 on 05/03/2013 15:55:35

David,

You should easily be able to hold a ruler to the nose thread and count how many crests there are in an inch; 8 and 12 tpi are pretty different.

Some threads are a bit too close to each other for such crude tricks to work. For future work you will find it invaluable to have a thread gauge - only a few quid, and should allow you to identify most threads. I suspect many of us have found it paid for itself in allowing us, over the years, to identify many of those bolts one finds lying in the road!

David

Edited By David Littlewood on 05/03/2013 16:24:04

Hi David,
In the last sentence of my last message I meant coarser (Not shorter as I said.)

In your last post to cut 12 TPI with an 8 TPI leadscrew you need to gear the leadscrew down by the ratio of 8/12 which is 2/3 which is also the same as 30/45 so these gears are correct. In your text the way you say the gears should be fitted is correct but your picture shows the larger gear on the spindle and smaller gear on the leadscrew. If you need to cut an 8 TPI thread then the gearing should be 1:1

I think you should measure the pitch of the thread on the spindle nose rather than relying on what you have read. If you have digital calipers then hold the calipers across one thread and press the zero button. Now put the calipers to span two threads. It will now read the pitch. (Spanning a number of threads and dividing by one less than the number spanned will give a more a more accurate result.)

You could also measure how far the chuck moves when it is undone by exactly one turn.

Les.

Edited By Les Jones 1 on 05/03/2013 17:14:24

Cheers guys much appreciated. Just about to go down the workshop I'll let you know how I get on.

Did an hour before the football started. Didn't manage to get to depth but I am going to call this cracked guys no parting what so ever. The thread profile is a little rough, I'll blame this on tooling and material (rock hard piece of shaft, all but run out of practice scrap!) I did measure the spindle nose and of the half inch that is threaded I count exactly Six crests. A little more practice and I'll be ready to complete

Poor pic quality sorry guys. Ordered my thread gauge looking at tooling now any thoughts fellas? I was looking at RDG brazed tooling? I can't thank you enough guys.

ATB.

David.

hi David,

From the photo it looks like you have the top slide set to the wrong angle. If you insist on using an off set top slide method (it really isn't the only way), you want the top slide set to half the thread angle not from the lathe axis but from the cross slide axis. Using the protractor markings you don't want 27.5 deg but 62.5 (BSW/BSF threads). in other words, swing the top slide to be in line with and over the cross slide, then move it back 27.5 deg. It is a common mistake to read in books about setting half the thread angle and assuming you read the protractor for this purpose, but it is not that simple. Following what you thought you read you will end up with an unequal thread.

Hope this helps.

chriStephens

Hi David,
I was assuming the spindle thread was an acme thread. As it is a normal thread the way I suggested to measure the pitch using digital calipers makes no sense as you could not measure the thicknes of the crest.

As you are cutting a 12 TPI thread with an 8 TPI leadscrew with care you should be OK disengaging the half nuts. Re engaging the half nuts will either be the correct position or half a thread out. If it engages half a thread out then you wil see the tip of the tool aligned with the crest of the thread rather than the trough. The next engagement point of the half nut would put it in the correct position.

Les.

I made this gauge **LINK** for BSW angle to aid my setting so all is correct. On my machine the protractor is infront of the compound when its paralell so I can do half instead of the full angle. I'll call this thread done guys thanks an absolute million for the help guys wouldn't have been able to do it with out. I shall add a final pic of the finished backplate when done hopefully over the week end.

Cheers.

David.

Edited By woody1 on 06/03/2013 19:24:56