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Thread: why cant I cut this thread?
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6th Oct 2018, 11:54 PM #1Senior Member
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why cant I cut this thread?
I have a Takisawa 1000D lathe and am attempting to cut a 16 TPI thread - I have the proper gears assembled in the gear train as shown on the info plate and the levers for threading in the appropriate position but cant seem able to cut 16 TPI
The thread chasing dial shows 24,21,20 and 18 and the appropriate alphabetical position to engage the dial - I cant understand why I cant engage anywhere as the sprocket engaging the leadscrew (24T) engages the fixed TPI leadscrew - does the fact that the chasing dial has only the numbers above mean I can only engage 24,21, 20 or 18 TPI? I am sure I haven't had this problem before so maybe I'm missing something?
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7th Oct 2018, 07:31 AM #2Pink 10EE owner
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I am a bit confused by your description.
If you have a metric leadscrew lathe, you can not use the thread chasing dial for an imperial thread.Gold, the colour of choice for the discerning person.
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7th Oct 2018, 10:59 AM #3Senior Member
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O.K. so how do I cut 16 TPI thread?
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7th Oct 2018, 03:38 PM #4Pink 10EE owner
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Also you are aware with metric chasing dials, you need different gears for the dial itself for different metric pitches.
Metric threading on a lathe is not as straight forward as native imperial threadingGold, the colour of choice for the discerning person.
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7th Oct 2018, 06:06 PM #5Member
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Forget about the thread chasing dial.
Engage the half nuts, take the first pass but stop the lathe at the end of the thread. (it helps to have a groove here just marginally deeper than the thread depth)
Back off the tool a little, then reverse the lathe till the tool clears the end of the thread.
Wind in the tool for a bit more cut and then proceed as for the first cut until you have cut the thread full depth.
DO NOT DISENGAGE the half nuts until you have finished cutting the thread.
The only tricky bit is stopping the lathe at the end of the thread. Use the lowest speed you have available as this gives the most reaction time.
Works for me.
Alan.
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7th Oct 2018, 07:29 PM #6
Hi Alf, Guys,
What Alan said !
What I do different is run the lathe backwards and cut away from the chuck, no danger of hitting anything that way.
Because I have an imperial lathe I have to keep the half nut engaged when cutting metric threads, exactly the opposite to you.
18-09-2018-3.JPG 18-09-2018-2.JPG
This is my setup. Here I'm cutting a 4-48 thread.
A spindle mandrel would be a good Idea ! I'll do a post on mine later.Best Regards:
Baron J.
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7th Oct 2018, 09:30 PM #7Most Valued Member
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I've got the same lathe but unfortunately my change gears aren't finished yet so I haven't done any thread cutting.
Mine has a 4mm pitch leadscrew, and these marks on the chasing dial and the plate next to it.
To be honest I'm not sure exactly what those markings mean, and doesn't sound like yours is the same.
Steve
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7th Oct 2018, 09:32 PM #8Golden Member
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You can still use the halfnuts to terminate the thread, you just gotta disengage the halfnut at the end of the thread and kill the motor, withdraw the tool, start the lathe in reverse and pick back up on the same number with the thread dial, make life easy and use position 1 on the tread dial
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7th Oct 2018, 09:57 PM #9Most Valued Member
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The numbers at the top are the number of gear teeth for the gear that goes on the bottom of the chasing dial that engages the lead screw, and beneath each of the numbers is the pitch of the threads that work with those gears to synchronize the dial with the thread that you are cutting.
The letters I assume ? relate to the thread cutting g/box, just a guess tho...
cheers,shed
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7th Oct 2018, 11:00 PM #10Most Valued Member
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Thanks Shed -I hadn't even thought about there being different chaser gears.
The letters on the dial look like they match the ones on the chart, but I'm not sure how you get the other letters. Possibly the dial is double sided, but I haven't removed it to check.
Guessing I'll need to make some chaser gears as well as change gears that are in progress...
Steve
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8th Oct 2018, 07:29 AM #11Senior Member
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Thanks Steve and guys
- I have set my change gears as per the imperial threading plate ie. 72,68,30 and 120 then B (LH lever) and and RH lever to the right -have put a 16 TPI bolt in the chuck but the tool does not match the bolt when engaged but according to your second picture I should be engaging at 'E' as my manual says I have a 24 tooth gear engaging with the lead screw - will try again later and report back - dont understand the difference when engaging the chasing dial as the half nut has fixed TPI to match the leadscrew
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8th Oct 2018, 12:28 PM #12Senior Member
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It doesn't matter where you engage the half nut TO START when cutting an imperial thread on a metric lathe or VV as it is totally impractical to think we can disengage and use the chasing dial so reversing the spindle is the only way. The chasing dial will only work cutting metric threads. All you will do is progressively chew the thread up by engaging out of pitch UNLESS WE ARE GOOD AT WINNING THE LOTTERY 100% OF THE TIME!!
Have a look at the calcs I have added. As can be seen, you would have to have a 127 tooth gear or multiple of to successfully track it. For the 6mm leadscrew the repeat distance to drop in is 762mm.
Hope this will clear up some of your problem. The MAZAK lathes had the same (similar) chasing dial as you have there. We had two of them at work with the same setup. Good machines although I didn't like the carriage hand wheel position!
Rusty
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8th Oct 2018, 01:13 PM #13Most Valued Member
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Yeah - IIRC I remember you, Bob or Joe setting up one of the lathes and showing us that 762mm trick many years ago.
Personally I totally avoid this sort of problem by owning both an inch and a metric leadscrew lathe. Problem solved (at the expense of space/money). And anyway the Monarch CY has a single tooth dog clutch and leadscrew reverse so you don't need to do anything much once you've set the disengaging stop. Pity it's in bits while I re-scrape the cross slide & top slide ways.
Some idiot wants me to cut a 1/2-13 (UNC) thread ATM. I've just convinced him that 1/2" Whitworth will do fine. I hate cutting threads with prime number pitches, I'd have to look at the manual.....
PDW
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8th Oct 2018, 01:36 PM #14Senior Member
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No probs Pete. On an imperial machine just engage on inch marks Although my Dashin Prince stuffs that one up! The whole numbers actually relate to 3/4inch spacings on it.
Bob still kicking in Qld somewhere. Lost Joe a couple of years back due to a fall.
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8th Oct 2018, 07:48 PM #15Senior Member
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O.K. guys,thanks for your input none of which has solved my problem - I was going to ask Steve if we could talk as he has the same lathe as mine but no change gears so obviously can't cut threads - I have triple checked my settings with my change gears and as I am cutting a stud without a runout groove I always retract the tool at the end and reverse the rotation direction - I just put a 20mm. piece of brass in the chuck, engaged the half nut and took a cut which gave me a groove of about 40 TPI ???My manual tells me the gear engaging the leadscrew is 24T and the panel near the halfnut engagement lever has underneath 24 the letter 'E' so I engaged at 'E' but still get 40ish TPI
I have cut threads in the past without any problem so keep thinking I have missed something but can't think what it would be - keep thinking please fellers The calculation by old rusty toolie , I can't see its relevance to my problem
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