Scalefour Forum

This contemplating supplying or buying form tools should be aware that there are two types.

The more obvious type. which the Late Joe Brooksmith provided for the Proto:87 SIG membership has a end cut out in the exact shape of the flange profile and is used to cut directly end-on inwards. The drawback is that the cutting depth pressure is extremely high due to the full size of the profile being cut simultaneously and thus puts quite a strain on the strength and rigidity of miniature lathes. Ditto for plastic centered wheelswhich have low radial compression strength. It is also virtually impossible to re-sharpen once worn.

The alternative, as once provided by Teichmann of Germany, has the two sides of the flange profile spaced on either inner side of a wider end slot. The profile is then cut by moving the tool sideways to cut one side of the profile and then moved back to cut the other side. This allows for a much lower cutter pressure and so can be used on much smaller lathes. It also allows for safer cutting of plastic centered wheels if the wheel can be clamped on the rim. The operator however has to control the amount of the sideways movement to avoid cutting the flange too narrow or too wide. So a little more skill is involved. I suspect that this type of tool could theoretically be re- sharpened in some fashion.

Running a batch of custom profile form tools commercially is usually expensive, so it's important to figure out which type is likely to be most useful before commiting.

Andy

Here's a description of the Teichmann form/profile tool (in German) on the left hand side of the page - hopefully it is legible to all. Teichmann is still in operation and still does produce a tool for HO-pur (near-equivalent to P87) - costs about 50 Euro or so.

The Teichmann tool looks to be quite straight forward to use. However it does not seem to incorporate the 20 degree angle we usually favour for the tread. Am I correct in thinking this or did I miss something?

Cheers,

David

David Knight wrote:The Teichmann tool looks to be quite straight forward to use. However it does not seem to incorporate the 20 degree angle we usually favour for the tread. Am I correct in thinking this or did I miss something?

The instructions assume that the 20-degree/3% angle is produced by rotating the toolpost.

Thanks Ivan. Looking at the image of the tool itself, it does appear possible to sharpen it by grinding the top face as the contoured part looks to extend down to the bottom.

Cheers,

David

If you have a Unimat SL like me the only way to produce a 20° angle on the tread is to rotate the headstock. Now my Unimat with its Sherline Chuck is very true and therefore I prefer not to disturb that setting, but in any event I have found that coning is not essential for good running; a parallel tread is satisfactory if not strictly ideal.

Note to Webmaster(s): Could this thread be incorporated into the other thread about form tools? It seems bonkers to have two seperate discussions about the same topic!

Philip

Sorry,

I'm only allowed to post on guest book topics.

Andy

Philip Hall wrote:Note to Webmaster(s): Could this thread be incorporated into the other thread about form tools? It seems bonkers to have two seperate discussions about the same topic!

I'm sure it can be when it's run its course. while it is live thats' trickier (it requires constantly moving/approving/adjusting) - since guests can only contribute in the guest book.

Proto87stores wrote:Sorry,

I'm only allowed to post on guest book topics.

Andy

As for all non-members.

I have often wondered whether the society should extend the non-member posting privilege to the "product information" section of the forum. I'm sure that are other nonmember product designers who have little known P4 supporting items in their repertoire, even though P4 is not their main thrust.

Andy.

David Knight wrote:Thanks Ivan. Looking at the image of the tool itself, it does appear possible to sharpen it by grinding the top face as the contoured part looks to extend down to the bottom....

I'll dig mine out again - if I can remember where I put it! - and take a few more photos.

If the Society sponsored form tool is specifically for modifying RTR wheels, then my USA RTR experience is that RTR wheel rims are commonly plated over some base metal. Re-machining the flange removes the plating there, opening up the wheel for corrosion.

Andy

Most of the wheels I’ve dealt with over the years are often brass or nickel or even die cast, never steel or anything that will corrode, certainly not in the locations we keep our models. It’s a pain if they are brass when the plating has gone but liveable with.

Philip

Respectfully, I have to differ due to my experience. Worn away plated brass wheels on my powered US streetcars accumulate crud very quickly on the uncovered brass and the surface rapidly becomes non-conductive., which plays havoc with pick-up reliability. I have had to replace all wheels in use with solid Nickel silver ones to keep them running. Passive vehicles may just cause dirty track, but powered vehicles are greatly compromised.

Andy

Yes, brass can tarnish quickly but it doesn’t corrode in the sense I understand corrosion eg rust etc. However I have found that polishing the tread helps, and I use a rubber wheel in a mini drill which is also useful to impart a better finish to some of our steel wheels.

Philip

As a late update to this, a P4 wheel profile tool popped up on eBay earlier in the week, so I bought it. The photos suggested it was in its original plastic holder and hadn't been used.

It's more of a profile than a form tool. Just a tiny gash in one end, angled at 20 degrees or so.

I'm not sure if this was one of the ones that was produced by the late Joe Brook-Smith as a short run many years ago.