Cutting metric threads

[Anonymous]

John,

Thanks for the hints, I'll have to give them a try. With the Coventry dies do you use the normal cutting teeth, or set the die at an angle so that the teeth that are normally used to guide the die are used to cut instead?

I'm puzzled as to why thread mills should be so expensive, after all they're not much more than a glorified tap. It could be partly explained by carbide versus HSS, but carbide end mills aren't that expensive. May be it's much more difficult to form grind carbide than HSS?

Regards,

Andrew

[Ian S CParticipant @iansc]

I'v got a boring bar that will thead cut 6 mm, its made from a 3" length of 1/4" HSS,2" of it are ground circular about 3/32" dia(maybe a little less), and the cutting edge ground to 60*, I'v not used it on metric threads, but on 1/4" unf. My previous attempt at small internal threads was a 5/16" BSF castellated nut for the valve gear on the compressor at a local engineering shop, they didn't think they could manage to do it, and no one had a BSF tap.

For the hydraulic cylinders, I'd be looking at brass tube, the inside of that is usually good enough to use as is.

For drilling flat bottom holes either get a slot drill the right size,or take an ordenarydrill bit, and regrind it with a flat end instead of the usual point, start the hole with a normal drill, once the cone is out to full diameter, change to the flat bit and finish the hole.  You could of coarse bore the hole in the lathe with a little boring bar.     Ian S C

 

 

Edited By Ian S C on 22/05/2013 14:25:26

[rebekah andersonParticipant @rebekahanderson95322]

This is the current gear set up. I know its not right for the thread cutting but which ones would i change?

please use idiot proof description lol

Edited By rebekah anderson on 24/05/2013 23:06:11

[John Stevenson 1Participant @johnstevenson1]

The 4 gears from the leadscrew backwards.

Very top gear is the spindle gear, this is followed by the two plastic tumbler gears which drive the output gear.

Can you check that the output gear has the same number of teeth as the spindle gear [ looks it ]

Then we need a list of gears you have in total counting the last 4 and a close up of the small gear that is on the output gear shaft to determine if they are pinned or keyed.

[MuzzerParticipant @muzzer]

How about you drill and tap an M3 x 0.5 hole into the end of a suitable blank eg 12mm x 12mm x 50mm, possibly with a larger clearance hole right the way through after the first 10mm or so. Then screw an M3 x 0.5mm tap into said hole so that 5mm or so of the nose protrudes. Hold in place with a grubscrew etc.

Could arguably turn the end of the toolholder down eccentrically to fit into the bore of the work piece, continuing the eccentric turning process until the threaded hole breaks through by a mm or two, thus exposing one set of (better supported) cutting teeth once the tap is inserted.

Grind the end of the tap to allow it to work up to the blind end. The faster helix angle of the 3mm thread shouldn’t be a problem surely, given the larger diameter of the bore. Obviously you set up for 0.5mm / turn and screwcut as normal. This is all far too fine scale for the likes of me!

Muzzer

[rebekah andersonParticipant @rebekahanderson95322]

They are keyed as follows:

Myford ml7/ml10 they are keyed with a 3mm/1/8" key way

[John Stevenson 1Participant @johnstevenson1]

In which case you can use standard Myford gears and for metric you need two 21T gears

[rebekah andersonParticipant @rebekahanderson95322]

They go where?

[Sub MandrelParticipant @submandrel]

> Making a suitably sized boring bar to take such bits might be difficult [where "difficult" rapidly approaches impossible].

But if you are only putting a few threads in the end of a tube and 1/8" bit angled at 45 degrees should let you aget about 3/16" in.

Best way to make a bar for small diameters (say 6mm) is to turn a disc say 5.5 mm in diameter on the end of some silver steel bar with a stalk perhaps 4.5 mm in diameter. Make the outside of the disc angled to match the thread form. Now make a slightly angled notch in the disc to create the cutting edge with some relief, harden and temper. Use in a standard holder for round boring bars. I have one of these and it works very well.

If it blunts, just lightly grind it and rotate in the holder.

Neil

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Stub Mandrel on 25/05/2013 16:01:11:

But if you are only putting a few threads in the end of a tube and 1/8" bit angled at 45 degrees should let you aget about 3/16" in.

Sorry; I can't grasp the geometry of that one … Grinding a 60 degree threading form on the tip of a 1/8" diameter bit angled at 45 degrees sounds very tricky indeed !

Best way to make a bar for small diameters (say 6mm) is to turn a disc say 5.5 mm in diameter on the end of some silver steel bar with a stalk perhaps 4.5 mm in diameter. Make the outside of the disc angled to match the thread form. Now make a slightly angled notch in the disc to create the cutting edge with some relief, harden and temper. Use in a standard holder for round boring bars. I have one of these and it works very well.

If it blunts, just lightly grind it and rotate in the holder.

Neil

Can't argue with that version, Neil.

MichaelG.

[Sub MandrelParticipant @submandrel]

Hi Michael,

OK it clearly wasn't perfect, and I no longer have it (it was tiny!) but I found an old picture of it.

Neil

[Michael GilliganParticipant @michaelgilligan61133]

Thanks Neil … That's pretty darned good.

I hadn't realised that you were using square tool-bits in your boring bar. For some unjustified reason, I had presumed you were suggesting 1/8" diameter.

Touché

MichaelG

[Ian PParticipant @ianp]

I must say I like Muzzer's idea of a well supported tap being used to cut internal threads. I have tried using a tap and even though I shortened it significantly I managed to break it taking very fine cuts.

Like Neil I also use a 1/8" square HSS in a 45 degree boring bar holder. The picture is of one I ground for an internal 220mm diameter 1.5mm pitch square thread (in aluminium and only 3 threads up to a shoulder)

Ian P

[Ian PParticipant @ianp]

Rebekah

Regarding your hydraulic ram cylinders, since you are making them from solid bar why not use a bar diameter large enough to make the end terminals integral? The end caps could then be male threaded plugs, one of them being drilled through for the piston rod.

Are the cylinders single acting or a double ended type?

Ian P

[rebekah andersonParticipant @rebekahanderson95322]

Hiya,

They will be double acting.

don't think that way would be benificial to the operation of the cylinder.

http://www.wpraez.de/xtc/index.php?cPath=13

This is roughly what I am aiming for but longer.

The bigger ones are as you discribe but these are some what smaller.

[Roderick JenkinsParticipant @roderickjenkins93242]

Posted by rebekah anderson on 25/05/2013 15:58:52:

They go where?

I sense you are not getting the answer you're looking for . Assuming that you have a fairly standard set of gears of 25-65 in steps of 5 then you can set up the gear train to give a thread pitch of 0.49956mm using a 30,45 and 25 as the drivers and 65, 55 and 60 as the driven gears.

From the picture of your lathe, you have a gear on the end of the spindle that then meshes with one of the tumbler reverse gears which in turn meshes with a gear of the same size as the one on the spindle. This gear is keyed to a gear which will be your first driver. The first driver will mesh with your first driven gear which will in turn be keyed to your second driver on the first stud. The second driver will mesh with your second driven gear which will be on the second stud keyed to your third driver gear. The third driver will mesh with the third driven gear which will be fastened to the end of your leadscrew. It does not matter which order the drivers and drivens are in and you may have to shuffle the gears around to get them to mesh and engage with each other, just make sure that you have kept the correct gears as drivers and drivens.

May I suggest that the book "Using the Small Lathe" by Len Mason is a very good introduction to lathes of this type.

Hope this helps,

Rod

[John Stevenson 1Participant @johnstevenson1]

The problem with Becky's ML2 lathe is that it can only one set of compound drivers, the ML7 has two sets and this seriously reduces the options on gear counts.

Ideally she would be better off if she made a new bango or adopted a ML7 one but for some making tools to make tools isn't the path.

[Roderick JenkinsParticipant @roderickjenkins93242]

OK. In that case Becky will need a 21 tooth gear. With 25 and 21 as drivers and 55 and 60 as drivens then we get a pitch of 0.505mm which is close enough for me. The principle is the same, just ignore the gears on the second stud, driven 2 is the one on the leadscrew

Rod

[Sub MandrelParticipant @submandrel]

Surely as both threads are being cut to match each other, 24TPI would be fine?

Neil

[JasonBModerator @jasonb]

Problem with 24Ttpi is the thread depth is approx twice 0,5mm pitch which eats into the tube meaning a thicker wall and less internal dia.

Given that its an imperial lathe I would just cut a hybrid 6.0mm by 48 or 56tpi or whatever is nearest from the gears you have.

J

[Ian S CParticipant @iansc]

The threads, not being standard, don't need to be 60* or 55*, but can be a shallow angle, as long as they are both the same. I thnk there is one of the tubing threads that is something like an 80* thread angle. Ian S C

[Grizzly bearParticipant @grizzlybear]

Ian SC, For degrees, try Alt+ 0176 ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° Regards, Bear..

[rebekah andersonParticipant @rebekahanderson95322]

So true, they can be non standard.

Slowly getting there with gears. ML 7 gears on a ML 2 lathe isn't standard I'm sure.

the two big gears are 100T if i read correctly.

[rebekah andersonParticipant @rebekahanderson95322]

So here is what i understand is what you guys are talking about.

 

Edited By rebekah anderson on 29/05/2013 21:01:41

[Roderick JenkinsParticipant @roderickjenkins93242]

You've got it ! Looks like it's currently set up for auto traverse, which is really just a very, very fine thread.

Rod

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