|Chris TickTock||01/08/2020 22:14:58|
|480 forum posts|
I have a die holder that holds 25mm dies. If a rod is held in the chuck on the headstock with a suitable champher it may be possible to make a thread at the correct angle.
That's more or less the extent of my knowledge as I tried to cut a 3/8 thread with the die in the tail stock chuck and the tail stock allowed to travel along its table when pulled as it cuts a thread. The metal I used was mild steel. What I found was by turning the headstock chuck carrying the stock iby hand via a bar it was nigh on impossible to cut a thread.
Question: Is the Sherline not powerful enough for such uses or is it an other issue. I suspect aluminium or brass might have been possible and smaller threads would yield better results.
Am I asking too much of my little Sherline?
I subsequently cut the thread by hand and it looks fine but was not easy even by hand.
Edited By Chris TickTock on 01/08/2020 22:16:16
|Ian P||01/08/2020 22:53:25|
2407 forum posts
I think you have answered your own question!
If cutting the thread by hand is hard, cutting it in the lathe will still be very a very taxing task for a small lathe. Please be kind to your lathe.
How did you hold a 1" die in the tailstock chuck?
3741 forum posts
You need a lot of power to cut a thread in a single pass
Hobby machines tend to use multiple passes with a single point tool
|Nigel Graham 2||01/08/2020 23:10:04|
|673 forum posts|
I am afraid you are a bit!
That is a fairly hefty thread for die-cutting on a small lathe, especially if the steel is not a free-cutting grade. Even my 5"-centre-height Harrison lathe might wonder what's happening. Aluminium and brass might not be that much easier.
I find often the tailstock die-holder loses its grip in the taper, which is not good.
I assume you are using a split die in its "open" setting in the holder for the initial cut, not making the mistake of using the die closed, or as I have known happen, using a die-nut.
You would be far better, if possible on your lathe, screw-cutting the bulk of the thread and using the die in the tailstock holder to complete the depth and profile; and that seems common advice on this forum. Done with due care gives a good, concentric thread without unfairly straining the machine and work-piece... or you.
If cutting a short thread to a shoulder, turn the machine by hand (with the power isolated!). Manually or under power, take nice gentle cuts with a "spring cut" at intervals. On my Myford 7 I usually use 0.005" depth cuts - say 0.1mm on a small metric lathe.
Still use the die open for that profiling, closing it only if necessary - sometimes the open setting will still give a free-running thread for a new nut used as a gauge.
|not done it yet||01/08/2020 23:16:10|
|4748 forum posts|
First question might be whether the die happens to be 25mm OD or a 25mm thread? There is a difference.
Guessing it might be a 6mm thread, or some such, as he mentions ‘dies’ not ‘die’, so the thread might be down to 3mm possibly? That makes it a bit of a non-question, if that is the case, so my suggestion is for the OP to go and hunt u-tube, read a book (or several), or try the smallest thread and work upwards.
|Mick B1||01/08/2020 23:43:21|
|1611 forum posts|
I think something's wrong - most obvious possibility being that the die's set considerably too tight. Or the steel might be more severe than mild.
For threads I can't die-cut under power, I'd usually start the die in the tailstock holder, or even in a normal die holder squared by the face of the tailstock barrel, then finish by hand in a vice. I'd only screwcut if there's no die, the thread's too large for the lathe to drive in a die, or I need it to be more accurate than I think the die will give me.
|Andy Carlson||01/08/2020 23:51:49|
|260 forum posts|
Maybe there is more than one type of tailstock die holder but the ones for my Cowells work well for smaller threads. They use the outside diameter of the tailstock barrel for guidance and slide along it as the thread is cut. A tommy bar provides the torque.
I cant recall whether I had the lathe running under power or used the nut that I made for the mandrel to drive it by hand, most likely handraulic to start off but maybe with some slow speed power once things were underway.
Not sure how the Sherline is for low speed torque but even if you do the job completely without power the die holder still has the advantage of holding everything in the correct alignment.
I was cutting an M6 thread though - a 3/8 thread involves shifting a good deal more metal and therefore maybe double the required torque so that may be pushing things.
My 3/8 BSW die is 1 5/16 diameter so it wont fit on the Cowells. The (hand) die holder for this size has much longer and thicker handles than the little tommy bar for the tailstock holder too, so 3/8 may be too much for a little lathe.
4658 forum posts
There are no stupid questions but yours sure is contradictory. If you are turning the chuck by hand, how can the lathe's power be even remotely relevant?
It's all down to the power of your wrist and/or the length of the bar you are using to turn the chuck. Obviously, it will need to be as long as the handle on a regular handheld die stock in order to get the same torque applied to the die.
One thing that will make life a lot easier for yourself is to turn the job's outside diameter down below the nominal size. For a 3/8" thread you said you were cutting, I would turn the OD down to at least five thou undersize, probably a bit more. You only need 65 per cent thread engagement to get 90 per cent of full strength -- plenty for all but the most stringent aerospace applications.
Also be sure to have the die in the holder right way round, with the tapered lead-in teeth leading the cutting effort.
If it's a split die, the adjusting screw or the screw in the holder will need to be set to spring it open for the first cut.
Use Trefolex or similar tapping compound to make life even easier. And be sure to use the half-a-turn-forward, half-a-turn backwards method to clear the swarf as you go.
You should get yourself a copy of "The Amateur's Lathe" by LH Sparey. He outlines a lot of these basics in the clearest way I have seen and is a wealth of useful tips and info.
And "The Amateur's Workshop" by Ian Bradley is similarly useful for the rest of the workshop tools and equipment. Both are cheap to buy and worth their weight in gold and more.
Edited By Hopper on 02/08/2020 01:39:42
|Paul Lousick||02/08/2020 02:47:18|
|1459 forum posts|
Use a sliding die holder in the tailstock especially on small threads in soft material that are too weak to pull the tailstock along. If the die does not travel with the cut it will just remove all of the metal down to the minor thread diameter and ruin hours of work. (don't ask how I know and what I said)
If the lathe is strugling to turn, do it manually by locking the chuck and turning the die holder by hand, backing off regularly to break the swarf.
|Bob Stevenson||02/08/2020 06:23:37|
|411 forum posts|
....Good advice as usual,...but the basics need reiteration....
1) Threading is perfectly possible on small lathes....I do it all the time.....It causes much grief for beginners.
2) Make sure that the stock and die are matched....refer to 'Zeus' which should be close to lathe always.
3)NEVER cut threads under power....it's not a good use of your time as failure costs time and materials.
4) ALWAYS cut one third revolution and turn BACK quarter turn to clear chips thoroughly.
5) ALWAYS use a cutting medium....traditionally 'tallow' but candle wax or even lard/dripping in extremity!
6) For first threading use ordinary die holder......use end of tailstock to steady holder accurately...make sure handle ends DON'T bash the lathe bed during cuts......use tailstock holders when you know what you are doing.....I don't know what I'm doing yet, so never use them!
18329 forum posts
Can a small lathe handle a tail stock die holder?
Yes for smaller threads and no for larger ones, just like asking it to take a 0.1mm DOC and a 2mm DOC.
For your 25mm OD tailstock holder and the minimum speed that you have I would suggest turning the spindle by hand in which case you are somewhat limited by the available leverage as turning the chuck by holding it is like using a short bar type die stock. A mandrel handle may give a bit more leverage but then you will start getting to the stage where the work will slip in the small chuck so may have to just use the tailstock holder to start teh thread and then move to the bench vice and a bar type diestock.
Pitch of the thread also comes into it, you don't say what 3/8" thread you were trying to cut. If it was say 40tpi ME then you may have managed it but if it were 3/8" Whitworth then little chance.
When I used to use the Unimat 3 I held dies in a bar type hand held die stock and used the end of the drill chuck with the teeth wound back to support the diestock keeping it square to the work and put one of the chuck tightening tommy bars into the chuck to give a bit more leverage. In use one bar of the diestock rested on the topslide so it did not rotate, right hand applied feed to the tailstock handle (tailstock locked to bed) and left hand turned the chuck.
|larry phelan 1||02/08/2020 08:25:49|
|770 forum posts|
I tried cutting 10mm thread under power on my 6 inch Craftsman lathe using a tailstock die holder and found it a waste of time. The machine just did not want to know. I suppose I could have cut it by turning the chuck by hand ect but I dont see the point in that. I made a dieholder with a guide into which I can fit different sized bushes which guide the stock into the die in a straight line, along the lines of a GB threading stocks. The result is that I get good threads every time
I believe you need a fairly big motor to cut under power. I might add that my die holder is not used in the lathe, just in the vise.
|Chris TickTock||02/08/2020 08:44:00|
|480 forum posts|
Points I picked up from which I will add to my notes;
from Bob; 1:matching stock and die
2:Never cut under power
3:Use Cutting medium
from Jason 4: the pitch of the 3/8 thread was probably too much to allow the torque on the lathe
from Hopper 5:Turn stock 5 thou under size
(Your right my post was contradictory as I did not fully understand if I should use power)
from Mick B! 6: I was guilty of pressing in a die that was too tight into its holder
So all in all your posts confirm most of what I suspected and have been a great help.
Thanks to all for posting
|5942 forum posts|
I'd go so far as to suggest that taps and dies shouldn't be used under power on a lathe.
There are many jobs, like threading, where lathes are best turned manually. And others where a dead lathe is ideal for work-holding during hand operations. Just because a lathe has a motor, you don't have to power it up. When I tap and die on my 1500W lathe it's almost all done by hand. One exception: I often cut threads under power with a single point tool and then tidy up by passing a die over them. Its safe enough to do a final finishing cut under power in the interest of speed, though I rarely bother. By hand is quick enough for occasional threads. Mass production is another story...
|Nigel McBurney 1||02/08/2020 09:24:03|
717 forum posts
Surely the problem in the original post is ,""the tailstock was allowed to travel along the lathe bed" this practice is wrong the tailstock must be locked firm, and the die holder allowed to travel on its mounting rod held in the taper or the tailstock chuck. the torque on the dieholder must be resisted by a tommy bar NOT the key/keyway in the tailstock barrel,When using the dieholder under power the torque can be resisted by a length of bar held in the tool post,the bar is parallel to the lathe axis . the type of thread is not mentioned,unified fine ,40 tpi ME ,or brass thread might just be possible but it is not good practice to abuse your lathe,the safety device could be that the steel rod usually slips in the 3 jaw chuck.
18329 forum posts
I don't see anything wrong with using a Die under power provided it can freely feed itself and there is nothing sticking out of the tailstock holder that could start swinging about like a tommy bar to snap your finger off and a reasonably slow speed can be used. I do it upto about 6mm in steel then I cat grip the holder anymore.
I don't reduce the stock diameter either and if you do be wary of the blanket statement "5thou smaller" as that could be a large percentage of the thread when working on clock size items
Edited By JasonB on 02/08/2020 10:20:31
5296 forum posts
Examine your die under magnification. Check it actually has cutting edges. Lots of cheap ones come with free extra metal (burrs) on the cutting edges so you need to do some Dremel grinding in the three holes. If you do not have a split die get an abrasive cutting disc and have at it it is virtually useless as is so nothing to lose.
|937 forum posts|
I am unable to cut a 3/8”BSF thread using a good split die in a good die holder mounted in the tail stock by hand. Full stop. I use a mandrill with a handle having a large swing - I just do not have the strength and I am a big person.
If I want to cut such a thread, and I will be doing so in the next few days, I turn a thread and use the die to finish it off.
|Chris TickTock||02/08/2020 14:11:39|
|480 forum posts|
Funny you should say that I am still really strong so that's 2 of us you say its too much of an ask as i attempted it.
|Chris TickTock||02/08/2020 14:13:17|
|480 forum posts|
Thanks bazyle, like the idea of splitting one. This one was though
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