The ongoing saga of John’s floor

[John Stevenson 1Participant @johnstevenson1]

[John Stevenson 1Participant @johnstevenson1]

So decided to treat myself to a couple of those magnetic pickup tools that ARC sells to try to clear up a bit.

 

Strong magnet inside a closed tube, stick where all the crap is and it all sticks to the tube, place over skip, pull handle and it all drops off – brilliant.

 

So Mark 1 test.

 

Open doors and decide to start in the front shop.

 

 

Starting to look a tat bit untidy, so a few applications of the bigger pick up tool and voilà.

 

Impressive or not ??

Just need to get the skip emptied now

John S.

 

 

[Martin WParticipant @martinw]

Hey John

 

Where is the skip parked as looks like you may have put some things in it I would be willing to recycle .

 

Cheers

 

Martin

[John Stevenson 1Participant @johnstevenson1]

I was waiting for that.

You are welcome to those bloody rotors, I’m getting decidedly pi$$ed with doing these.

24 got dropped off today with end covers and wanted back for Monday.

 

Spent all afternoon making an 8 start nut 1″ lead and 1/2″ diameter, right pain in the butt but came out nice.

 

 

Hopefully Mr Rolls Royce will be able to get his crack testing machine working again tomorrow.

 

John S.

[Anonymous]

Ok John, so I can think of ways to machine an eight start screw, but how on earth do you make the nut?

 

Andrew

[John Stevenson 1Participant @johnstevenson1]

Not by CNC

I’ll throw it open first for all the manual guys to have a guess.

John S.

[haroldParticipant @harold]

I’d always assumed that tales of the existence of this floor were cruel myths.

We now know that the floor does exist.

Another myth busted.

Another entry for snopes.

 

John

[Tony JeffreeParticipant @tonyjeffree56510]

I always thought saga was an old English name for rice pudding…

 

Regards,

Tony

[Nicholas FarrParticipant @nicholasfarr14254]

Hi John, I’ve not done any multi start screw cutting, but as for the eight start nut, how about fixing the mandrel gear to an index bush/plate of some kind, so it could be adjusted without loosing position on the leadscrew.

 

Nice lot of rotors BTW.

 

Regards Nick

[blowlampParticipant @blowlamp]

Posted by John Stevenson on 09/06/2011 09:04:33:

Not by CNC

I’ll throw it open first for all the manual guys to have a guess.

John S.

 

You’ve gotta tap!

 

Martin.

 

[John Stevenson 1Participant @johnstevenson1]

No no tap and no spare bit of screw.

 

The screw in question is the only bit, it’s 4 feet long and has a bearing diameter at both ends.

 

John S.

[David Clark 13Participant @davidclark13]

Hi John

I would think move the top slide along by one 1/8inch for each pitch until you have cut the thread in 8 different places. Probably have to leave the leadscrew engaged depending on pitch of the leadscrew. If the leadscrew was 1/8in. pitch, you could probably use all eight markings on the thread indicator, the numbered ones and the halfway between ones.

I could of course be totally wrong and probably am.

 

regards David

[Tony JeffreeParticipant @tonyjeffree56510]

Posted by David Clark 1 on 09/06/2011 12:58:07:

I could of course be totally wrong and probably am.

 

regards David

 

Fraid so David.

 

But then, John told me how he did it the other day – and a very useful technique it is too. When he first mentioned the problem to me, my immediate reaction was “Use Moglice”, but that wasn’t how he did it either.

 

Regards,

Tony

 

 

[Tony JeffreeParticipant @tonyjeffree56510]

Posted by harold on 09/06/2011 09:13:54:

I’d always assumed that tales of the existence of this floor were cruel myths.

We now know that the floor does exist.

Another myth busted.

Another entry for snopes.

 

John

It doesn’t really exist. Photoshop can do some wonderful things these days…

 

Regards,

Tony

[Ian S CParticipant @iansc]

My guess would be a broach of some sort, rotated as its drawn through the hole. The external thread I would expect to be done on the mill, but what do I know? Ian S C

[Anonymous]

Well, you could use a helical broach, but I suspect it’s not the sort of tool you have lying about on the off chance.

 

Could use EDM, but again not the sort of machine most people have.

 

It would be possible to do it on the lathe, but it would be a funny looking tool to get the right clearances. More of a shaping action. So it could be done on a shaper or slotter with the right feed mechanism.

 

It could probably be done on a manual mill if the nut was split and done in two halves.

 

However, the nut looks like plastic or anodised aluminium?

 

If plastic then the thread could be made by a heated screw, or a simple home made broach.

 

But, since this was presumably a repair job, and was done in an afternoon, I prefer the ‘slap some goo around the screw and make a moulding’ approach. Could use resin or one of ‘liquid metals’ for better strength.

 

Whatever way, it’s out of my league.

 

Regards,

 

Andrew

[Jim CozensParticipant @jimcozens]

I think if I were going to attempt this and assuming there was a piece of the external thread available as a gauge I’d screwcut off 7 of the 8 starts with a suitable grooving tool just leaving one. This would enable each start to be gauged. For each pitch advance the top slide by .125.

 

Regards,

Jim

[John Stevenson 1Participant @johnstevenson1]

Jim,

No spare thread to hand but I like your reasoning.

 

John S.

[Jim CozensParticipant @jimcozens]

John,

Only other way I can think of with no gauge but the finished male part is to take a pass  through each start at each depth of cut. Bit of a chore but at least all the starts would be at the same depth. Take the tailstock off if necessary to make room to get the 4 foot long screw lined up to test the fit.

 

Jim

Edited By Jimbo on 11/06/2011 10:50:52

[Richard ParsonsParticipant @richardparsons61721]

So you have a ‘bit’ of the 8 start thread. Oh ‘goodie-goodie’! I would a bit of it to the rear of the head pipe and using the bottom of the thread as a ‘dividing head’. I would use it to set and then cut no 1 ‘start’ thread to depth. Disengage the saddle nut, rotate the head stock 1/8^th of a turn, re engaging the saddle, and cut start no 2 to depth. Repeat as required until all 8 starts are cut. I would use the other bit of the spare thread as a gauge. I can repeat this procedure ad-nausiam until I got a good fit.

But as usual there is another way! This is to cast the nut using something like ‘Babbit’ or ‘Hoyte’ metal (or the thermo setting plastic if that is what it is).

I am going to have to use this method sometime next year to restore cross slide nut on my 36 year old Myford – it is getting a bit sloppy.

ATB

Dick

Edited By Richard Parsons on 11/06/2011 13:31:05

[blowlampParticipant @blowlamp]

Assuming the old nut was still usable: Bolt it to your miller bed and in alignment with the (also bolted down) bore of your new nut. You could somehow attach a single point cutting tool to the end of the threaded rod (a bit like a between centres boring bar) and use it to cut one of the starts. Repeat the operation seven more times by indexing the threaded rod within the old nut.

 

Martin.

Edited By blowlamp on 11/06/2011 14:17:51

[John Stevenson 1Participant @johnstevenson1]

Watch the lips.

 

NO SPARE BIT OF THREAD, JUST THE 4′ SCREW.

 

Tony mentioned the cast method using Moglice and whilst I can’t see a problem with it I don’t have any and couldn’t wait for a delivery.

 

Old nut not usable, it was in made two pieces, one piece threaded into the alloy retainer, M24 x 1.5 and the other somehow fasted to it to form an adjustable anti backlash arrangement but something had broken off when it completely stripped the thread out of one half and the other has about 1/4″ of linear play.

 

Amazing how it had managed to keep working.

 

The new nut is black oil filled Delrin.

 

John S.

[VersabossParticipant @versaboss]

Aah, Delrin!

So you possibly warmed the screw to 150 or so deg. and pressed two pre-formed oversize Delrin blocks around the screw? After this, machine the outside(s) to measure.

Greetings, Hansrudolf

[John Stevenson 1Participant @johnstevenson1]

Hansrudolf nearly has it.

 

Been around for a while and I believe it was ‘discovered’ by a guy called Darryl on the Practical Machinist forum to give the correct credits.

 

Get a block of Delrin and bore a hole thru it with a diameter halfway between the OD and the root diameter, in my case this was 7/16″, not too critical, then split the block from one side to the centre.

 

Open the gap up with a couple of screwdrivers and force the screw in with about 3″ or so sticking out one end.

 

Then clamp the split up in the vise and heat the screw with a hot air gun equally from both sides and keep the vise tight. Eventually after about 20 minutes the gap will be closed and you will see some melted Delrin at the ends.

 

DO NOT try to wind the screw thru as it will rip the thread out, it needs to be static.

 

Once done and cooled down in my case I drilled for two clamp screws and one central jacking grubscrew so the preload can be set.

 

John S.

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