Trevor

you still have the same travel surely

you now go from 0" on the scale rather than 1"

but you run out at 3" rather than 4"

I would keep the quill deeper in the tailstock

Hi Trevor,

For small trapezoidal pitches you may be able to cut them with one tool. For larger you first use a tool resembling a parting-off tool – as you say, and finish with two tools that cut the angle part on each side.

Here is a link you may find useful, it is primarily for Acme but the technique is the same.

Thor

Chinese and modern but hey still make more for the US market so some parts may still be imperial.

As to the shape of the tool (never having cut one of these threads myself).. then from the top It's going to be a 29 r 30 degree point truncated at the tip either as a very shallow radius or as a flat with two tiny corner radii. From the front it's gong to look thinner at the bottom than the top but the front edge will 'lean' by the lead angle. You need to dig out a chart for that angle to add and subtract from the side rakes of your 29/30 deg tool for the material you cut and to find the width of the tip 'flat'. You'll be feedng it in at roughy half that 29/30 deg angle for most of the cut then going in square with the cross slide for the las pass or two as a straight form tool (so the half angle doesn't have to be perfect)

I'm fairly new at al this too. 'Tom's techniques' (youtube) describes shaping thread tools a lot better than I do and after following his tutorials I happily single point any i don't have a die for (lazy when possible)

…or ypu buy a length of acme/trapezoidal allthread <g>

I had my first go at cutting a square thread for my hardness tester. I ground the tool from a piece of 3/16" dia. hss. I think I used 2 degrees relief all round. The width is slightly less than the 1/16" that the 8tpi needed so that I could shave the last few thou off to measure to the correct size. You can rotate the tool in the holder to get the correct angle to give you relief on the cutting edge. I was pleasantly surprised how easy it was to cut the square thread in EN1A. If I was cutting an acme or trapezoidal thread then I would rough out using this tool to the correct depth and then grind a second tool to the correct form to finish off.

HTH

Rod

I have recently cut a trapezoidal thread for my Warco 220 lathe. This was a 12mm dia x 2mm pitch RH thread for the cross-slide leadscrew and was about 130mm long.

The tool was ground up from an old file as best I could (tip width was supposed to be 0.6784 mm wide so I made it almost 0.68mm wide) and has a 30 degree inclusive angle. I slowly cut the thread using my minimum speed (125rpm) increasing the depth of cut by 0.05mm or 0.1mm at a time until I reached the required depth of 2mm. This was actually the third attempt, the first I made a mess of and broke the tool, and the second being experimental was deemed a success as it almost fitted first time. This, third attempt, worked first time. I haven't actually finished what I'm doing but see no reason why it shouldn't be a success.

I used EN1A.

I see no reason why a LH thread should be any different – it just means that the clearances etc are the other way and the leadscrew turns "backwards" rather than "forward".

Regards,

Peter G. Shaw

I would if I were you. It's not difficult just fiddly when the od is being turned initially.

There is a decent video on use that shows setting up better than this one – but notice the comment about bulging in the middle on this without one – even on 12mm

**LINK**

This one shows screw cutting with one – where you really are likely to need it

**LINK**

Doubleboost is usually pretty good. On that one I would be inclined to work away from the chuck with a centre a bit loosely set. The reason being that the bar is being pulled throughout the cut – not pushed which might cause it to bend if there is any lathe misalignment. If the centre is well out of alignment it will have to be used to just stop the bar whipping about and not really be in contact with the work at all. Strange things can happen if it is. The centre will be trying to keep the work in one place and the steady in another. On that basis it could be argued that it's always best to work away from the chuck. You'd best have a play around as you might find best results are obtained when the slides are a little loose – depends on how precise the lathe is. When the same principle is used on a well worn capstan lathe I have seen both the chuck and the saddle move when the work went into the cutter box – good accurate parts came out as what the machine does hardly matters.

They give a rounder and more consistent size plus a better finish with sensible cuts that force the work up against the steady – this is also why the work comes out round and the same size all along if done correctly.

Boxford never updated their steady for modern tool posts. It's for a lantern type but I reckon it could be used with a qctp by using the side away from the chuck or angling it etc but the steady jaws ideally need to very close to the cutter.

John

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Your problem is the length of the 2MT sleeve(Is your's one with a tang?), it should be an open one.

Ian S C