Thompson Class B1 Springbok

[stevep]

May 11, 2023 10:27:19 GMT Shawki Shlemon said:

Its strange , I tried both works . Thanks anyway .

I think that it's because the link you gave takes you into your account to edit the video, rather than the public 'view and play' of Youtube.

[hunslet]

A few years ago at the Harrogate show i got talking to a chap who was buildind the Martin Evans Springbok. He very kindly sent me a list of the known problems with the design. Here are those two sheets. I am unable to attach the information sheet as apparently this forum has reached its file limit, oh well

[mbrown]

Like many new members, I also got caught out at first by the auto response saying the forum was full.

Look at the thread on Posting Photos and that gives clear instructions how to do it using a hosting site.

Good luck.

Malcolm

[jinks82]

I have spent many hours looking for details in respect of the cock fitted to the forward facing cylinder cover. Does anyone have any details? Are they available as an accessory?

[jinks82]

This may be a silly question. In accordance with Martin Evans drawings I have only fluted my con rod on one side. As a result the rod has now become bent by 2 or 3 mm. My question is this: Would fluting the rear of the rod restore the bend of should I gently coax it back to straightness by bending it back? What about heating it up before bending. A lot of time goes into making these and I don't want to scrap this rod.

I would be grateful for any suggestions

Steve

[ettingtonliam]

If you have access to a set of bendin rollers, just ease the rod trouh them. Don't heat the rod now but it miht have helped if you had annealed the bar stock before machinin the rod.

[uuu]

I have straightened things - and watched John the Pump (he's good at it) in the fly press. Although it seems like a brute of a tool, you can build up a feel for the amount of strike and it's highly repeatable. Only doing a short part of the length at a time. You can start light and get a sort of bounce going, where you're not taking it beyond the yield point and work up. Somehow you can "feel" the moment when there's a slight change and, sure enough, it's a little bit straighter. Work your way along gently gently - and after a while you can't tell it was ever bent.

Of course practice on something else first!

Wilf

[jinks82]

Many thanks chaps! I was thinking of using my mill/drill machine and slowly applying pressure using the hand feed with the rod sat upon a parallel bar at each end. What do you think? I don't have a fly press or bending rolls. I will definitely take on board the suggestion of annealing before machining next time!

[uuu]

The danger trying to do the whole length in one go is you keep the curve over most of the length, but get a kink in the middle. And doing a short bit at a time you need a higher force than might be sensible in your mill drill.

But you could have a go with a spare bit of metal to see if you can control it. Perhaps using the fine feed graduations to add a thou at a time and see if you can find the yield point.

Wilf

[brucevoelkerding]

I agree 100% with Wilf. You will not get the Rod straight by just trying to support the Ends and applying a Force in the Middle. However, you will be just exceeding the Yield Point to get the Rod straight - don't worry, the Steel will locally work-harden - it will not affect the function of the Rod (in 5" Gauge). I had to straighten a Part similar in size to your Rod. I Duct-Taped 2 Pins vertically on the back Jaw of the Bench Vice, approximately 2-1/2" center-to-center. I then Duct-Taped a third Pin vertically on the moveable Vice Jaw and equidistant between the other 2 Pins. The Pins were about 1/2" diameter. They were probably Dowel Pins I found lying around.

Using the Process mentioned above by Wilf, I went along the Length of the Part. It was easy to judge what was going on as you can look down on the Part as you try straightening it. You do get a feel for the Process plus the Vice Handle gives an Indication how far you go on each Pass. Use large diameter Pins to minimize bruising the Rod. Go slowly and check your Progress on the Surface Plate.

[chris vine]

Or you could hang some bits of metal in the vice: 2 at the back jaw, at either end, say 3 inches apart. 1 in the middle of the front jaw.
Then you can use the vice to apply the pressure. You might need someone to help you hold the rod, or put some bits of metal underneath to guide it.
Again, little and often and work your way along. It does work, I have used this dodge in the past as I don't have a fly press...

Chris.

[miken]

Sept 24, 2024 10:15:00 GMT jinks82 said:

This may be a silly question. In accordance with Martin Evans drawings I have only fluted my con rod on one side. As a result the rod has now become bent by 2 or 3 mm. My question is this: Would fluting the rear of the rod restore the bend of should I gently coax it back to straightness by bending it back? What about heating it up before bending. A lot of time goes into making these and I don't want to scrap this rod.

I would be grateful for any suggestions

Steve

I made my B1 nearly 30 years ago (it's been in regular use ever since fhen) I too fluted my rods one side only and they also bent (I made all the rods from stainless steel).  I just bashed them straight with a mallet and a vice.
I've built a few more locos since then with similar results and cures.

[Shawki Shlemon]

I experienced this early days of my hobby ( over 40 years ago ) , since then if I use mild steel I normalise the flat bar before machining and distortion will not happen , alternatively if I use black cheap steel I just machine it without treatment . Most of the time I only flute on one side , one can not see the other side . I personally would make a new one but may be someone can suggest a good method to straiten it accurately .

[uuu]

Beware also that the length of the rod may have changed during the fluting. Coupling rods the wrong length are a pain, connecting rods less so.

For this reason, I've taken to finish-boring the holes after all the shaping.

Wilf