PTFE die block

I felt a bit disappointed that the PTFE die blocks that I used will have to be replaced before doing any useful service. The pin that goes through the block into the radius rod yoke has created an oval hole and this will affect the timing. I think the problem is the small dimensions of pin and block; a 3/32" pin through a 3/16" wide x 1/4" long x 1/8" thick block. Nice idea if it worked. Back to the steel.

Any thoughts?

Dave

Hi Dave,

I use bearing grade PEEK which is a harder material. I think virgin PTFE is probably too soft for such a highly loaded application and it will just deform, hence the oval hole.

John

Has anyone tried Tufnol (synthetic resin bonded fabric) as used to be used for example for contact breaker cams in motor cars?

Andrew M

Thanks folks. John, do you have a prefered supplier for PEEK?

Dave

Speaking of die blocks and difficulties therewith, I remember reading on this forum a more or less throwaway line from someone who said that he made circular die blocks. There was no further comment on this but it seemed like a good idea to me and I subsequently made up some circular bronze blocks, 1/8" diameter, for the Walschaerts gear of a Gauge 1 loco. They seem to roll perfectly and the timing is consistent but it has yet to run in steam. Has anyone else used this idea?

Mick

Hi Dave ,

In the past I've bought it from RS. They have Tecapeek PVX in 10mm diameter. They don't seem to have the range of diameters that they used to have though.

**LINK**

I've also bought it from Davis Industrial Plastics when I wanted longer lengths. They have PEEK HPV:

**LINK**

Both are similar materials. It's very expensive in larger diameters but not too bad for small stuff. I'm sure there will be other suppliers if you look around.

I use it for all sorts of bushes on locos e.g. coupling and connecting rod bushes.

Mick - I haven't tried round die blocks as such but over the pond they seem to use them quite a bit, even on 7-1/4/7-1/2" gauge stuff.  I have used a round die block in the slots on the end of a radius rod with good results

John

Edited By John Baguley on 11/05/2014 09:18:18

David,

PTFE will creep unless constrained.

René Etter (RSME) did extensive experiments using the stuff in making D valves, and found this problem.

Cannot remember if he found a solution or not, but I think details where published in ME in the '70s or early '80s.

Geoff - Time to get wet plugging exhaust leak. Oh the rain has eased.

I used a material called Orkot for my die blocks on my 4" Garret, after having used it at work on something subjected to severe loads on a feed chain, where it stood up very well. These die blocks have been in since 1997, and there is no noticeable wear to date. The material has graphite in it I believe which helps with lubrication. I have used the same material for my 6" Garret 4CD die blocks. It is available, and a google search will give some suppliers. There are similar materials out there.

Chris Gunn

Dave,

I have had excellent service from this ebay seller.

MichaelG.

David, Having had a look at MichaelG's link, the Orkot is similar to the Ketron Peek HPV.

Chris Gunn

Getting a bit complex, you might over come the tendency to oval holes by using a metal bush in the hole, or salvage one that has acquired an oval hole. Ian S C

Hello David

PTFE will always creep, It also smears under load, I have found that out the hard way making slider blocks on a machine.

Can you post a photo of your die? I have an idea but cannot visualise your design.

Regards
John