Small taper pin turning

Hi I need to turn a few replacement taper pins, 1 in 20 taper by about 3mm (thick end) and 20mm long. Easy enough to turn with the compound slide set over. The problem is I haven't a clue how to set the angle accurately enough - I just cannot set it to two decimal places of accuracy! I haven't got a sine bar (and doubt if I would know how to use it anyway!) Thought I could turn a larger diameter piece (having calculated the small and large diameters at a fixed length) but can forsee problems accuratley measuring the 'small' end becouse of the taper.
Don't know if I'm missing the obvious - anyone got any pointers please? Its only a one-off job so don't really want to have to spend too much time. I only want a couple & assume I'd have to buy a 100 or something readmade ones? Many thanks for any replies regards Mike

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Could you get the accuracy you want by mounting a dial gauge on the tool post and then adjusting the angle of the compound slide until you get the desired difference in diameters?
Cliff Coggin.

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If you have one good pin then this is nasty but works for me: set the slide to somewhere close. Turn your stock down at that setting then lay (or clamp) pin alongside. If correctly set then DTI on saddle should give zero change along taper length. Adjust until it does.
hth

I spoke tripe.Early dementia! The two outsides of the tapers will be parallel.
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Surely you were right the first time, the DTI would only read zero movement if the turned taper is exactly the same as the pattern taper when laid/clamped beside each other, in a reverse taper manner. If the turned taper was out, the DTI would show an error when the pattern was clamped to it. Bob
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Do he arrows below show you the answer? i.e. Roland was right second time.
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Henry

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I see your point now, so surely if the original taper was held in a chuck and clocked along the length, and say for example, the needle moved 5 thou over the length, an incorrect taper laid beside it, clocked in the same way on the "incorrect" taper, would make the needle move more, or less, than the 5 thou depending on how far out it was? I never did like taper work, and you can see why !!! Bob
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Better expressed as? 1 Clock taper pin when true in chuck to measure taper. 2 Set lathe to reproduce taper as well as possible. 3 Replace taper pin with blank material and turn a taper. 4 Lay original taper pin alongside and check for more or less taper than the original.
However why not just clock the material being turned in step 4? I suspect that one problem might be holding the original true unless it has an untapered end and isn't bent or otherwise mangled.
What it is to theorise! Henry

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How do I check the smallest diameter? Because of the taper, neither my Micrometer or digi calipers will give a true reading at the 'small' end. Feel that I'm failing to 'see the light' here! Mike

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Maybe I haven't grasped the problem completely, but if you know the taper you want then the method I suggested should work. You only need to set the slide angle while holding a parallel rod of any size in the chuck. For greater accuracy adjust it for a taper of 5 in 100 rather than 1 in 20. Substitute a tool for the dial gauge, and the work piece for the parallel rod, and turn an overlong pin. Fit the pin in its hole and cut to length.
On the other hand if you don't know the exact taper and just want to match an existing pin, then the method suggested by Roland should work.
Cliff.

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My favourite method is effectively a sine bar but homemade. The idea came from an article I read somewhere, but I cannot remember the source.
Make a bracket which can be placed against a part of the top slide which is parallel to its motion. The precise arrangement depends on whether this is dovetailed or square. If square a piece of cleanied up angle, if dovetailed, you need a piece of ground steel (e.g. silver steel) inside the angle to make sure the reference is taken from the side of the dovetail rather than the corner which might be a bit worn.
Fit two vertical pins (I used 1/4" silver steel) so that the line of the pins is parallel to the top slide motion. Mine are 2" apart. Measure distance of centres and turn up two discs with holes reamed to fit over the pins such that when the bracket is on the top slide and the discs are on the pins touching a true bar in the lathe, the tailstock is at the correct angle.
The true bar could be the tailstock barrel if this is parallel to the mandrel (!), or a bit of silver steel in a collet in the headstock.
The bracket takes a little time to make, but it is very handy for lots of other tapers.
Alan

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Meadows and Passmore carry stocks of taper pins, roughly £3 per 100 (or 50), in my view hardly worth making if they have the size you want in their range.
Pat

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I have enough grief from the wife as it is about 'all that rubbish you keep in the garage' that I have to try & maintain minimum 'stock' of everything! (Mind you - isn't it funny that when shes says "... oh, my such & such has broken,..." and I usually manage to disappear into my 'rubbish vault' and it 'magically' comes out mended - she never has much to say!). So, another tin of 98 unused taper pins will just take more shelf space for years to come! Throw them away? Sorry thats very much against the grain! It's the usual story - I just want a couple of simple bits for a job, and the obvious solution is a quick 'turning job - its not until you stop and think about what you are trying to do that it starts to become an interesting 'challenge'. Thanks for all the ideas folks, I'll look into your suggestions. All the best Mike

MikeH_QB wrote:
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A suggestion:
I have seen something like the following described but have not tried it myself.
Put a piece of stock - say 0.5" - in the chuck with 6" or so sticking out. To be extra sure put it between centres so that it really is parallel to the lathe bed.
Arrange the topslide to be parallel to the lathe bed. This is easily done with a DTI in the toolpost, reading against the stock.
You could use the DTI from there but the following might be easier.
Lightly clamp a square in the tool post so the long edge lies along the axis of the top slide. Mark a position 100mm away from the corner on the outside of the blade. Rotate the topslide so that the corner of the square touches the stock and a 5mm drill bit is trapped between the blade and the stock at the 100mm mark. This should set your topslide angle to pretty well 1 in 20. To be more accurate, use two drill bits, say 1mm and 6mm, 100mm apart. Of course you will probably have to use at least three hands to get that right.
Pete Harrison

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It crosses my mind that there is a more significant issue...
1:20 is not a standard taper.
1:48 is for imperial taper pins 1:50 is for metric taper pins
You wouldn't get commercial pins at 1:20 anyway.
Are you sure of the taper?
As to turning them. Put a piece of parallel bar of the right length between centres, complete with driving dog. Offset the tailstock so that a DTI on the (in line) top slide shows 1 thou per 40 thou of movement (for 1:20 included). Then turn the bar until the diameters are what you want. Lather rinse and repeat (identical lengths of pre-centered bars for efficiency).
Mark Rand RTFM

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You might be right you know! May be a misprint in the original document identifying the mechanism components, because thinking about it 1 in 20 does seem quite a sharp taper! I don't want to remove the original until I was sure that I could fabricate a new one properly.The original is jammed up quite badly in the inner component, but loose in the outer one. It's almost certain to be unusable again once I've forced it out. If it does appear to be a 'funny' size, I'll possibly use a taper reamer and re-cut the hole to a metric 'standard' if I can, and use the ideas you guys have posted to make new pins. regards Mike

*Small taper pin turning*
I need to turn a few replacement taper pins, 1 in 20 taper by about 3mm (thick end) and 20mm long. Easy enough to turn with the compound slide set over. The problem is I haven't a clue how to set the angle accurately enough - I just cannot set it to two decimal places of accuracy! I haven't got a sine bar (and doubt if I would know how to use it anyway!) Thought I could turn a larger diameter piece (having calculated the small and large diameters at a fixed length) but can forsee problems accuratley measuring the 'small' end becouse of the taper.
Don't know if I'm missing the obvious - anyone got any pointers please? Its only a one-off job so don't really want to have to spend too much time. I only want a couple & assume I'd have to buy a 100 or something readmade ones?
A method that I saw used many years ago to copy a taper was as follows:-
1)    Ensure that the tailstock and lathe chucks are truly in alignment 2)    Chuck a piece of bar a bit larger than the taper pin and longer than the jaws of the tailstock chuck. Turn the outside true 3)    With a sharp drill a fraction larger than the small end of the taper pin make a shallow depression in the end of the bar – the idea is to produce a bowl for the pin to locate in 4)    Part off the machined length of bar 5)    With a sharp drill a fraction larger than the large end of the taper pin make a shallow depression in the material left in the chuck 6)    Hold the first piece you made in the tailstock chuck 7)    Grip the taper pin between the tailstock and lathe chucks 8)    Mount a dti in the toolpost at centre height 9)    Adjust the topslide angle so that the dti registers zero along the lenth of the pin 10)    Turn your taper pin
This method does need one good taper pin to work from and a dti that does not apply too much pressure to the pin as it is only resting in shallow locations.
John

Mike,
You haven't said what the pins are for. If it is clock making...
John Wilding recommends making your own in the lathe using a pivot file (No 6 cut) and a broach to fit them, but I ordered a bag from Meadows and Passmore. I've been struggling to find a supplier of swiss needle files in different cuts (from 2 to 8).
Cheers
Mike

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For clock work the taper isn't critical so pins can be filed by hand without a lathe.
Cousins do a good range of files. I recently bought a selection of escapement files from them at about £12 each.
Cliff Coggin.

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Thanks Cliff. That's a supplier I hadn't found. They have a great range of tools.
Mike