Internal threading on Alu tube problem.

[Martin BrundellParticipant @martinbrundell]

Hi, got a bit of a problem I need to find a solution for:

 

I have several 350mm x 38mm OD x 35mm ID Aluminium tubes that I need to put a 0.75 metric thread inside the ends (10 – 15mm depth). I have a wm280VF lathe that only has a 26mm spindle bore.

 

I dont currently have a fixed steady (looking to get one) but even if I did would it help?

 

Advice please on the best approach as I have never done anything like this before. (I’ve threaded externally and internally on small stuff using the lathe)

 

thanks

[Martin BrundellParticipant @martinbrundell]

[JasonBModerator @jasonb]

Yes you can do it with the steady no problem as this will allow you to hold one end of the tube in the 3 jaw and the other end in the steady. Or make up a steady yourself.

 

A more complicated solution would be a threading tool held in a boring head in the lathe spindle and clamp the tube using V bocks and packers to the cross slide and feed that onto the rotating tool at 0.75mm / rev. If you don’t have a boring head then a bit of your 20mm steel could make a between cts boring bar to hold a threading tool.

 

Jason

Edited By JasonB on 03/05/2011 20:02:24

Edited By JasonB on 03/05/2011 20:06:19

[Les Jones 1Participant @lesjones1]

Hi Martin,

The way I’m going to suggest I have never heard of anyone trying before.

The basic idea is to mount the screw cutting tool in a boring head in the headstock and mount the tube on the cross slide. The hay I would mount the tube is to get two lumps of wood. The first lump with a height that makes the top surface sit at the centre height when mounted on the cross slide. First find a way to clamp it to the cross slide. If the cross slide has T slots then use four studs to fix it. The second block of wood should be about 60 mm thick. Before mounting the first block on the cross slide drill holes to allow four more studs to bolt the two blocks together. I suggest using the type of T nuts that press into the holes in the wood in the lower block. Now clamp the two blocks together on the cross slide. Tighten up the gib on the cross slide so it cannot move. Now drill a large hole in the blocks with a drill mounted in the headstock and open it up to just under 38 mm with the boring head. This hole will be concentric with the spindle. Slacken the studs holding the top block of wood to the bottom block and slide the tube into the hole and re tighten the studs. DO NOT SLACKEN THE STUDS HOLDING THE BOTTOM BLOCK TO THE CROSS SLIDE.

Now put the screw cutting tool in the boring head. You should now be able to cut the thread.

Les.

[JasonBModerator @jasonb]

Posted by Les Jones 1 on 03/05/2011 20:15:09:

Hi Martin,

The way I’m going to suggest I have never heard of anyone trying before.

Think thats what I just said

 

Martin if you look at this and the next two photos it shows the wooden block arrangement that Les describes, the block was actually used on a smaller lathe but are posed for the photo on the 280.

 

J

[Les Jones 1Participant @lesjones1]

Hi Jason,

Looks like I’ve just re invented the wheel.

Les.

[JasonBModerator @jasonb]

Shall we just settle on great minds think alike

J.

[Martin BrundellParticipant @martinbrundell]

Trying to digest this – i get the idea of the tube locked into a wooden holder on the slide (ingenius) – however struggling with the boring tool holder. Does that actually spin in the headstock? How do you change thread depth?

 

thanks

Edited By Martin Brundell on 03/05/2011 21:02:12

[Martin BrundellParticipant @martinbrundell]

Right got it as I have seen the adjuster on the boring head thanks

 

Do you know anywhere that does a straight boring head arbor?

 

brill thanks again

[Les Jones 1Participant @lesjones1]

Hi Martin,

I assume you want a straight boring head arbor so you can mount it in the chuck. I have not seen these advertised. If you take the chuck off your lathe there is normally a morse taper in the end of the spindle so you should be able to get a morse taper arbor to fit. (You may have to use a reducing sleeve.) By the way I think the use of spacers as shown in the second picture that Jason pointed to is better than boring the hole slightly under size as I suggested.

Les.

[JasonBModerator @jasonb]

Chronos do boring heads with a set of arbors so you can change between straight & MT. But I would suggest you get a 2″ head with MT3 arbor and then get a open MT4 to MT3 sleeve from Arc euro which will allow you to mount any MT3 tooling in the spindle. If your lathe is not the Warco and only has a MT2 tailstock then get MT2 instead.

 

If you look at my last picture you can see a between centres boring bar, the allen screw locks a HSS toolbit which could be ground as a thread form tool, this can be adjusted to make the cuts in several steps by advancing the tool out of the holder though a boring head is a lot easier.

 

Personally I would buy the steady as its going to be more use than the boring head on the lathe. This shows how the steady is used to supportthe end of a tube.

 

J

 

 

[Michael Cox 1Participant @michaelcox1]

test post

[Martin BrundellParticipant @martinbrundell]

Right great thread and thanks for the info – working on it now.

 

thanks

again

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