Author Topic: Pottymill telfon and crank questions  (Read 4571 times)

Offline tinglett

  • Full Member
  • ****
  • Posts: 255
  • Rochester, MN, USA
Pottymill telfon and crank questions
« on: October 21, 2014, 08:23:47 PM »
While I reorganize my shop and tune up my lathe a little bit, I thought I'd look ahead to what I think will be my next build...the Pottymill engine.  It was designed by Stewart Hart and was drawn by Julius over at http://www.modelenginemaker.com/index.php?topic=1388.msg59921#msg59921

My first question is about teflon.  The plan calls for three rings made from teflon.  Here are excerpts, including a little context where they go:


It seems clear to me they are designed to be nice slippery rings to hold compression.  Can these be purchased (reasonably) pre-made, or is this something I should machine?   If I search for "PTFE rod" I get a hit on eplastics.com which seems to be a reasonable supplier for me in the USA, provided I can machine this stuff, and if I can re-work the plan to imperial measurements.  Anyone know of other, better sources?   I haven't checked eplastics to see how/if they handle a tiny order.

Another question is on the crank.   Here's an excerpt:


I assume I should create this as three parts that are either silver soldered, or threaded and loctite'd together.  I'll prefer the latter as I've never silver soldered anything yet.   Is there another way?  I'm raising the question because the drawing doesn't provide a suggestion, but perhaps this is normal to leave unspecified.

My last question is why it might be called a "Pottymill engine."   Looking just now, I see Stewart's original print says "Pottyengineering" and "Potty trilogy of engines."  I guess I'll need to do some searching to find the other two in the trilogy.  There must be a story behind this...just curious :)

While I'm on the topic, has anyone out there built this engine yet?  Any words of warning?  I've only built three oscillators so far, so hopefully I'm not going over my head.  It looks like a reasonable engine for my skill, and I really like the look of it, but I might be missing something.  Here's a rendering of it from Julius.  Pretty spiffy if you ask me.



Todd

Offline Bluechip

  • Full Member
  • ****
  • Posts: 821
  • Derbyshire
Re: Pottymill telfon and crank questions
« Reply #1 on: October 21, 2014, 08:46:24 PM »
Todd

I have machined PTFE, not as readily turned as Delrin but much easier to get a good finish than nylon. One suggestion is make sure the cutter is dead sharp, preferably HSS and honed to an edge. Not had too much luck with CCMT inserts but the ones specifically for aluminium  ( may ) be better. Maybe make them from PTFE sheet, 0.5mm, 1mm and 2mm is readily obtainable in UK so it should be OK in the USA ?? UK Link:

http://www.directplastics.co.uk/ptfe-sheet

The 'VETON' ring may be a misspelt 'VITON' ie. an O-Ring ??

Silver soldering not my province ...  :headscratch:

Dave

Offline Jasonb

  • Full Member
  • *****
  • Posts: 6773
  • Surrey, UK
Re: Pottymill telfon and crank questions
« Reply #2 on: October 21, 2014, 08:47:37 PM »
Take a look at Stew's original build thread, it shows how to machine all the parts and I think he used O rings. The "Potty" bit is explained in one of his build threads.

http://www.modelenginemaker.com/index.php?topic=1801.0

The second engine in the series

http://www.modelenginemaker.com/index.php?topic=2890.0
« Last Edit: October 21, 2014, 08:59:08 PM by Jasonb »

Offline tinglett

  • Full Member
  • ****
  • Posts: 255
  • Rochester, MN, USA
Re: Pottymill telfon and crank questions
« Reply #3 on: October 21, 2014, 09:07:29 PM »
Well, how cool is that!?  Build logs! :)

I skimmed Dad and Lads a bit and saw how he turned the connecting rod.  It really is turned as one part.   I wasn't sure how the round end would be shaped, but it makes reference to a filing button.  I'd never heard of that before.  A few searches and I've already learned something new!  Nice.  I was thinking maybe it could be finished on an RT.  I suppose that might work, too.

I'll look at sheet plastic too.  For the piston rod and valve rod seals, they could be punched out since the outer diameter isn't that important.  I don't think I'd get away with that for the piston ring, though.

Todd

Offline derekwarner

  • Full Member
  • ****
  • Posts: 529
  • Wollongong ...... Australia
Re: Pottymill telfon and crank questions
« Reply #4 on: October 21, 2014, 09:53:16 PM »
Todd.....

A 6-033 standard size o-ring is 13 ID x 1.5 section...so would suit the nominated piston cavity & be available in VITON & as Jason notes........O-rings may have been used
For added preload...you could marginally increase the 13 dimension of the cavity

In Australia...[being part metric] the electronics shops sell 3x6x0.5 nylon spacer washers as electrical insulators

Derek
Derek Warner - Honorary Secretary [Retired]
Illawarra Live Steamers Co-op - Australia
www.ils.org.au

Offline b.lindsey

  • Global Moderator
  • Full Member
  • *****
  • Posts: 13759
  • Dallas, NC, USA
    • Workbench-Miniatures
Re: Pottymill telfon and crank questions
« Reply #5 on: October 22, 2014, 01:14:35 AM »
Todd, you might check PM Research Inc. for Teflon rings. They don't show them in their catalogue but supply them now with their casting kits and should have several US sizes like 5/8", 3/4" and probably 1". If they have a size you could use I expect they would sell you a few and you could adapt the ring groove width and depth to match what they have. Just an idea.

Bill

Offline steamer

  • Global Moderator
  • Full Member
  • *****
  • Posts: 10412
  • Central Massachusetts, USA
Re: Pottymill telfon and crank questions
« Reply #6 on: October 22, 2014, 01:21:24 AM »
Teflon works well, but it really needs an expansion ring if you want to run steam.    If your running air it's not that important

making one with a lapped split isn't as hard as you might imagine.....think about it for a minute and you'll see it

"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline b.lindsey

  • Global Moderator
  • Full Member
  • *****
  • Posts: 13759
  • Dallas, NC, USA
    • Workbench-Miniatures
Re: Pottymill telfon and crank questions
« Reply #7 on: October 22, 2014, 01:31:55 AM »
Dave, wouldn't a 45 degree angle cut for a joint be just as effective and easier to accomplish. I ask that not to debate but to learn the answer.

Bill

Offline steamer

  • Global Moderator
  • Full Member
  • *****
  • Posts: 10412
  • Central Massachusetts, USA
Re: Pottymill telfon and crank questions
« Reply #8 on: October 22, 2014, 01:40:15 AM »
It would be easier to make, but it wouldn't allow for the thermal expansion that Teflon has.  It needs room to grow, and a 45 wouldn't do that unless you left a bit gap...and that wouldn't seal well

It's really not hard to do if you think for a minute..... :LittleDevil:


We all need a puzzle to think about every once in a while....

Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline b.lindsey

  • Global Moderator
  • Full Member
  • *****
  • Posts: 13759
  • Dallas, NC, USA
    • Workbench-Miniatures
Re: Pottymill telfon and crank questions
« Reply #9 on: October 22, 2014, 01:45:44 AM »
Thanks for the info!  Been way too long a day to day to think on it tonight, I'll keep it in the puzzle queue though :)

Bill

Offline steamer

  • Global Moderator
  • Full Member
  • *****
  • Posts: 10412
  • Central Massachusetts, USA
Re: Pottymill telfon and crank questions
« Reply #10 on: October 22, 2014, 01:57:59 AM »
 8)

Thanks bud!.....I'll let you guys in on it tomorrow if your stumped....not that hard though...but does take a bit of basic math.
If you can work Pi x D = C....you'll have it

Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline sbwhart

  • Full Member
  • ****
  • Posts: 712
  • Live Long and Prosper
Re: Pottymill telfon and crank questions
« Reply #11 on: October 22, 2014, 06:54:56 AM »
Hi Thanks for all your interest in my little engine.

To answer some of the ?.

1:- Yes there have been lots made, it was serialised in the Model Engineer and has proven to be a very popular engine for the beginner, as I designed it its very robust to the odd mistake and all the material can be easily obtained

2:- Julius drew the engine up with some of his own ideas/interpretations so its not has I drew it and I'm not Shure if an engine to his drawing has been built. If anyone wants a copy of my drawings all they have to do is drop me a PM with you email address and I'll send them.

3:- I didn't use Teflon seals I just used graphite yarn or you can use PTFE tape just twist it into a rope and use that its cheep and easily obtainable no need for expensive seals, the idea was for an engine that was easy to built and didn't use expensive material.

4:- The pottyengineeing came from my working days as a design and development engineer, the guys on the test beds use to tease us by saying hay up her comes some more potty ideas this then evolved into pottyengineering, for you Guys across the pod in this context it has nothing to do about going to the toilet (rest room), its all to do with something that's a little crazy and out of the ordinary.

5:- As for the trilogy of engines I wanted to design a sequence of engines that used a lot of common parts the mill engine was the first of the trilogy the second was my cross vertical engine see picture, the third will be a grasshopper engine that I will start shortly as soon as I can get my Bloody loco Running.



Stew
« Last Edit: October 22, 2014, 07:12:33 AM by sbwhart »
A little bit of clearance never got in the way

Offline tinglett

  • Full Member
  • ****
  • Posts: 255
  • Rochester, MN, USA
Re: Pottymill telfon and crank questions
« Reply #12 on: October 22, 2014, 04:24:52 PM »
Dave,
The lapped split ring is nice, but probably a bit beyond my ability of today...but I could certainly try :).  I'd have to do the math to get the diameter right, but I can see that would have the nice side effect of making it easy to install as well.  I assume when it pinches to fit it will stay concentric enough to seal nicely.

Stew,
Thanks for the background!  I've got a much better grasp now that you've answered questions and now that I've looked through the logs of the other two engines.  I'll definitely try your technique of turning the connecting rod.  I was also too distracted by the "teflon issue" to notice you have created a packing device for the seal.

As for the name, I should have done more searching.  I assumed the definition on our side of the pond was wrong, but I knew it was going to be a FAQ when I label the engine as "Pottymill" so I thought I'd better get the answer!   Anyway, searching for a definition got me the right hit on the first shot:

pot·ty
adj. pot·ti·er, pot·ti·est Chiefly British
1. Of little importance; trivial.
2. Slightly intoxicated.
3. Somewhat silly or crazy; addlebrained.

Todd

Offline Roger B

  • Global Moderator
  • Full Member
  • *****
  • Posts: 4086
  • Switzerland
Re: Pottymill telfon and crank questions
« Reply #13 on: October 22, 2014, 07:26:39 PM »
I had assumed (always dangerous) that Potty came from your name being expanded to Stewpot and then to Potty  :Doh:
Best regards

Roger

Offline sbwhart

  • Full Member
  • ****
  • Posts: 712
  • Live Long and Prosper
Re: Pottymill telfon and crank questions
« Reply #14 on: October 23, 2014, 07:10:26 AM »
Hi Roger

The only person to call me Stewpot/Potty was the manager of the test facility so I guess that's where the link came from for pottyengineering, though I can't remember what came first,  everybody else since I was a kid called me Stew. but to be honest you can call me what you like as long as you don't call me late for dinner  :ROFL:.

Stew
A little bit of clearance never got in the way