R.M.S. die.

Here you can suggest and discuss Websites, books, and other resource materials.
Post Reply
Message
Author
apochronaut
Posts: 2731
Joined: Fri May 15, 2015 12:15 am

R.M.S. die.

#1 Post by apochronaut » Mon Jun 10, 2019 2:16 pm

Does anyone on this forum have or have access to an R.M.S. objective thread die?

PeteM
Posts: 646
Joined: Tue Dec 06, 2016 6:22 am
Location: Santa Cruz, CA

Re: R.M.S. die.

#2 Post by PeteM » Mon Jun 10, 2019 8:12 pm

Phil, Don't know about a die - the taps are readily available. However, most lathes will cut a 36 tpi thread and it's not hard to shape a tool to the 55 degree included (vs. normal 60 degree) angle. Perhaps someone in your area has a shop? One minus to a die is that they usually can't cut cleanly right to a shoulder -- so you may be better off with a lathe-cut thread with a bit of relief next to any shoulder that might be present.

MicroBob
Posts: 1487
Joined: Sun Dec 25, 2016 9:11 am

Re: R.M.S. die.

#3 Post by MicroBob » Mon Jun 10, 2019 8:26 pm

Hi Phil,
here RMS taps and dies are offered: https://www.baercoil.com/pdf/Gewindebohrer2014EN.pdf
Price on request, propably dirt cheap! :mrgreen:
I don't know what quality would be to expect there. It isn't an established manufacturer, maybe better chinese quality?

Are you up to an interesting project, by the way?

Bob

MichaelG.
Posts: 1485
Joined: Mon Apr 10, 2017 8:24 am
Location: NorthWest England

Re: R.M.S. die.

#4 Post by MichaelG. » Mon Jun 10, 2019 9:41 pm

MicroBob wrote:Hi Phil,
here RMS taps and dies are offered: https://www.baercoil.com/pdf/Gewindebohrer2014EN.pdf
Price on request, propably dirt cheap!
Infinite Improbability Drive engaged:
https://baer.tools/en/taps-dies/thread- ... 8-x-36-hss

MichaelG.
Too many 'projects'

apochronaut
Posts: 2731
Joined: Fri May 15, 2015 12:15 am

Re: R.M.S. die.

#5 Post by apochronaut » Mon Jun 10, 2019 10:46 pm

Thank you for the answers. Not an interesting project. I'm stalled on the previous interesting ones. If I take on a new interesting project, it will dilute the interest yet again and leave less interest available for each project. Diluted interest eventually becomes unstable, allowing enthusiasm to escape as a vapour. The residual substance left behind is apathy.

I just have a brand new bright phase contrast objective that was finished with a stirrup type mount. The flange is big enough to accept about 4 R.M.S. threads and there is a clear space behind it Pete, so a die should have enough room to produce a finished thread.

All of the sources I have seen, Baer being one, show extremely high prices. I just thought if someone happened to have one, I might be able to rent it or hire it out.
A lathe is possible and I have access to one but I probably should take all the optics out, which makes it more of a project. A die would be a 1/2 hour job. max and the optics could stay put with a bit of protection.

tgss
Posts: 86
Joined: Wed Jan 25, 2017 3:48 am
Location: Ontario, Canada

Re: R.M.S. die.

#6 Post by tgss » Mon Jun 10, 2019 10:57 pm

I have never used an RMS die, but the diameter is large enough that I suspect it would be quite hard to hand start the die square to the axis of the part being threaded. Even if used in a lathe dieholder the depth of thread is such that getting a clean result in one pass on a blank diameter would be unlikely. Ideally the thread should be rough cut by screwcutting on the lathe using a tool as suggested by PeteM, then finished accurately by removing the last few thou with the die.

Tom

PeteM
Posts: 646
Joined: Tue Dec 06, 2016 6:22 am
Location: Santa Cruz, CA

Re: R.M.S. die.

#7 Post by PeteM » Mon Jun 10, 2019 11:25 pm

Interestingly, at least for me, the price Baer wants for a single RMS die should buy a lathe capable of cutting a lifetime of 36 tpi threads.

Phil, a possible hack would be to get a $10 parfocal extender with RMS threads. Probably already have one - you'll just need the threaded portion. Then turn down the diameter of what you have to slip fit inside the parfocal adapter. Bit of epoxy and you now have your RMS threads. This means pretty much any lathe with a collet or chuck (or a mill) capable of holding what you have could be put to use.

Depending upon the objective (needs a cylindrical section), I've had good luck holding them with collets. If the lathe bore and collet are clean, there's no damage from the inside and it's usually possible to block the backside of the objective from any chips. And with a proper cutting tool, the chips will peel off safely away.

I've also cleaned up the barrels of not-so-pricey objectives by screwing them into a parfocal extender and holding that in a collet. Takes some care not to get any grit near the exposed lens, but this dodge has helped get a few more microscopes out the door and into the hands of kids. So far no damage to any glass, though I wouldn't likely try it on a pricey objective.

Might also add that a lathe collet is a superb tool for removing a stuck objective from its mount.

MichaelG.
Posts: 1485
Joined: Mon Apr 10, 2017 8:24 am
Location: NorthWest England

Re: R.M.S. die.

#8 Post by MichaelG. » Tue Jun 11, 2019 5:27 am

apochronaut wrote:If I take on a new interesting project, it will dilute the interest yet again and leave less interest available for each project. Diluted interest eventually becomes unstable, allowing enthusiasm to escape as a vapour. The residual substance left behind is apathy.
:o Wow ... I didn't realise there would be free psychoanalysis on this forum

MichaelG.
Too many 'projects'

MicroBob
Posts: 1487
Joined: Sun Dec 25, 2016 9:11 am

Re: R.M.S. die.

#9 Post by MicroBob » Tue Jun 11, 2019 7:43 am

Hi Phil,
cutting the thread with a die would lead to quite big cutting forces. I'm not sure that the barrel really is intended to withstand them. On the other hand side sigle point cutting on the lathe is a very fine process when done in several cuts (and always stopped before the shoulder). For this small amount of thread it would be sufficient to use a metric lathe and choose a pitch that is close.
Typical dies also need some turns to cut to full depth so the last threads to the shoulder might no fit into every nosepiece.

Bob

MichaelG.
Posts: 1485
Joined: Mon Apr 10, 2017 8:24 am
Location: NorthWest England

Re: R.M.S. die.

#10 Post by MichaelG. » Tue Jun 11, 2019 8:17 am

MicroBob wrote:For this small amount of thread it would be sufficient to use a metric lathe and choose a pitch that is close.
Although, in pragmatic terms for a one-off job, you are probably right, Bob
It is interesting [nay, humbling] to note how closely toleranced the RMS threads were specified.
http://www.science-info.net/docs/etc/RMSthread.jpg

I have seen a set of the inspection gauges ... a thing of great beauty!

The suggestion made by PeteM makes a lot of sense to me [*], and a suitable grade of Loctite 'retainer' would be my favoured fixing method.

MichaelG.
.

[*] although I would probably just use an optically scrap objective as the thread donor
Too many 'projects'

MicroBob
Posts: 1487
Joined: Sun Dec 25, 2016 9:11 am

Re: R.M.S. die.

#11 Post by MicroBob » Tue Jun 11, 2019 9:18 am

Hi Michael,

0,003 inch tolerance is 0,0762mm, this is actually a comparatively coarse tolerance for todays standards. At the time this standard was defined the lathes will have looked "somewhat" different though. I couldn't find a date for this standard. Maudsleys invented the lead screw around 1800 it might have been before this date. Precision machining was an art at this time!

Petes suggestion is very good as it reduces the turning operation to a very fool proof one - always a good thing.

Bob

MichaelG.
Posts: 1485
Joined: Mon Apr 10, 2017 8:24 am
Location: NorthWest England

Re: R.M.S. die.

#12 Post by MichaelG. » Tue Jun 11, 2019 9:49 am

MicroBob wrote:0,003 inch tolerance is 0,0762mm, this is actually a comparatively coarse tolerance for todays standards.
Very true, Bob ... but impressive for the time
I think I have a note of the date, somewhere
... Will edit this post if I can find it.

MichaelG.
.

Edit: see here: https://onlinelibrary.wiley.com/doi/pdf ... .tb01530.x

Edit: see here pp39-41 for the original 'standard'
https://www.biodiversitylibrary.org/ite ... 9/mode/1up
... I note with some amusement that they quote 54° thread angle ... but presumably Whitworth put them right.
Last edited by MichaelG. on Tue Jun 11, 2019 10:59 pm, edited 1 time in total.
Too many 'projects'

apochronaut
Posts: 2731
Joined: Fri May 15, 2015 12:15 am

Re: R.M.S. die.

#13 Post by apochronaut » Tue Jun 11, 2019 12:36 pm

MicroBob wrote:Hi Phil,
cutting the thread with a die would lead to quite big cutting forces. I'm not sure that the barrel really is intended to withstand them. On the other hand side sigle point cutting on the lathe is a very fine process when done in several cuts (and always stopped before the shoulder). For this small amount of thread it would be sufficient to use a metric lathe and choose a pitch that is close.
Typical dies also need some turns to cut to full depth so the last threads to the shoulder might no fit into every nosepiece.

Bob
I'm not anticipating any undue cutting forces. The thread is very fine, so intrinsically requiring less force, going onto brass and there will be only about 4 of them; not requiring anywhere near the force encountered by most of the other threads I've cut in the past. This is also a fairly beefy, one piece barrel : not one of those thin walled cores with the external cosmetic sleeve and I probably can grip the flange, when turning the thread. Quality dies can also be adjusted for depth, finishing the thread in more than one cut.

Whitworth threads are difficult to cut on a lathe. I know that people make do with metric lathes but the crest and root have a rounded form. This posed so much of a problem that the ASME developed an alternative truncated thread in 1958, that allowed the use of conventional machinery to make microscope threads. The truncated thread ANSI B1-11 1958 (1972) presumably became adopted . I haven't looked at any of my American made stuff closely enough to see if the crests are flat. The truncated thread crests pose zero problem in this application, it's not like they are being used to mount rocket launchers, so I probably could get someone to use that form, since I have the specification. I do have access to a shop that cuts Whitworth threads for aircraft parts, so I could go there but the objective isn't important enough to me, to spend 50.00 or more to thread it. It just has the correct specs. on the barrel, so I would like to use that barrel. If I can't get a thread on it easily, I will just swap the optics over to a plain barrel, which would render it fully functional. The two barrels are identical; just one has bright phase, stamped on it.
Last edited by apochronaut on Tue Jun 11, 2019 3:22 pm, edited 1 time in total.

MichaelG.
Posts: 1485
Joined: Mon Apr 10, 2017 8:24 am
Location: NorthWest England

Re: R.M.S. die.

#14 Post by MichaelG. » Tue Jun 11, 2019 3:18 pm

apochronaut wrote: Quality dies can also be adjusted for depth, finishing the thread in more than one cut.
Unfortunately, the one listed by Baer is clearly shown as being solid.
... I have seen no documentary evidence, but I presume that they expect it to be used for finishing a thread that has already been partially screw-cut.

MichaelG.
.

Edit: regarding the truncated form ... I think it useful to post these links:
https://www.ring-plug-thread-gages.com/ ... -B1.11.htm
http://gost-snip.su/download/ansi_b1_11 ... twe_thread
Too many 'projects'

MicroBob
Posts: 1487
Joined: Sun Dec 25, 2016 9:11 am

Re: R.M.S. die.

#15 Post by MicroBob » Tue Jun 11, 2019 5:25 pm

apochronaut wrote:Whitworth threads are difficult to cut on a lathe.
Today there are full-profile rungsten carbide inserts that cut the rounded root and crest when the last cut is made. Whether these are easily available for this thread is the next question.
With home shop equipment I would use a tool with rounded tip and cut the thread on a slightly oversize diameter. When I then turn it down to a bit over size and gind it zo size with emery linen I would come very close to the perfect profile.

Post Reply