Cutting an M33 x 3.5 thread on my ML7

[Howard LewisParticipant @howardlewis46836]

As a backplate for a chuck, there is no reason why the hole needs to be blind. So the thread can pass right through, making life so much simpler..

Having cut the thread, and measured the diameter, and depth, of the register on the Mandrel, the backplate can be screwed onto the mandrel in reverse, so that the register can be accurately bored into it.

Once this has been done, the backplate can be screwed on to the mandrel in the normal way. It is now ready for the O D to be turned to the size needed to provide an accurate fit in the chuck. Once this has been done the backplate can be faced so that its face is square to the axis of the mandrel, and is the correct thickness for the chuck in question.

The only job remaining is to mark out and drill the holes for the fixings..

Chuck and backplate can then be united and used a s complete unit.

Howard

[Mike PooleParticipant @mikepoole82104]

My thinking on a backplate or faceplate thread is that a loose fit is more desirable than a tight fit, my thoughts are that the register should not be fighting the nose thread, the threads job is to hold the faceplate against the register and does not play a part in the true running of the faceplate. The effort needs to be put into getting the registers right rather than a showpiece thread.

Mike

[Howard LewisParticipant @howardlewis46836]

As Mike says, the register is the all important part of the job. A bit of clearance in the threads will allow the registers to perform their function and locate the chuck accurately.

Howard

[Thomas CooksleyParticipant @thomascooksley79020]

Hi Captain, we have all got tied up in cutting this thread and how it mates with spindle on your new lathe but how are you going to hold a steel blank large enough to turn a face plate out of on your Myford ML7? it's not going to fit in the chuck. IMO your only chance would be if you already have a face plate for your Myford then you could bolt your work piece to that. It would need to be very carefully balanced as well, that lump of steel is going to weigh several kg's and you don't want that getting out of balance on your lathe.

Tom.

[HopperParticipant @hopper]

Posted by Thomas Cooksley on 03/08/2020 21:39:11:

Hi Captain, we have all got tied up in cutting this thread and how it mates with spindle on your new lathe but how are you going to hold a steel blank large enough to turn a face plate out of on your Myford ML7? it's not going to fit in the chuck. IMO your only chance would be if you already have a face plate for your Myford then you could bolt your work piece to that. It would need to be very carefully balanced as well, that lump of steel is going to weigh several kg's and you don't want that getting out of balance on your lathe.

Tom.

Bolt it temporarily to a piece of smaller diameter round and hold that in the chuck.

[Captain BarnaclesParticipant @captainbarnacles]

Well I got around to trying thread cutting yesterday and it went … OK-ish

Actually, for my first time I was quite happy with the results. With my lathe I inherited a mountain of tooling, most of which means nothing to me (yet!). I had a rummage around, found what looked like an external thread cutter and mounted it the lathe. I set up the appropriate change gears and loaded a piece of 12mm mild steel bar in the chuck.

I suspect that the cutter wasn't a sharp as it could have been but I still got a result of sorts.

Onwards and upwards with a few more practice runs before commiting to a proper lump of material. I may also invest in a couple of replaceable tip thread cutters to make life a bit easier.

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