ST governour

I am making a governor for a ST engine . the part calls for a 3/16 brass tube 2 inches long , bored 1/8 and threaded 1 inch at 40 tpi . I have tried 3 times , but each time it distorts under its own weight I tried boring first , tried threading first tried inching it out ot the chuck . I don't have a fixed steady , Theading with a tailstock die holder . I am going to try in steel tomorrow , but it must be doable , where am I going wrong ?

Regards Phil

It is indeed possible, I did it many years ago. Make sure your 3/16" x 40 Die is sharp and open it right up for the first cut then a couple more cuts until the nuts fit on.

Should not need a fixed steady and you probably only need 3/4" length of thread.

Agree with Jason. The die must be sharp. Some die holders can also be a little tight on the die. This does not allow you to open the die enough.

Maybe you could make the bore smaller than called for to achieve the thread? 

Bri

Edited By Boiler Bri on 29/04/2019 20:05:40

The final wall thickness is not much. With 3/16 OD and a 1/8 bore the wall is going to be 0.03125 thick, and the ME40 thread depth is 0.016, so you will only have 0.01525" as a minimum thickness. This is not not going to be strong enough to withstand any heavy handed work, or blunt dies.

Take things very gently!

Howard

How about turning a length of brass rod to be a close fit in the bore and supergluing it place as temporary support during threading? Heat destroys the bond.

Leave a bit protruding to make the rod easier to remove.

Dave

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"tried boring first , tried threading first"

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Does it have to be 1/8" bore or will 2.5 mm or, better 2 mm work well enough?

Calling out a minimum wall thickness of 15 thou is, frankly, looney tunes unless you are set up to chase the thread with a proper attachment. Even then its not the easiest of things unless its what you do a lot.

Yes it can be done with great care and a really sharp die but this hobby is supposed be about enjoying making things not frustration, suffering and (loud) workshop language.

If I had to do it I'd probably make the initial bore 2 mm, thread it, support the whole thing in a tube as suggested by SOD with the end tapped to ensure the thread was well supported and drill out to size. The weakest loctire will be more than strong enough.

Clive

Personally I would stick with the 1/8" as the rod passes right through and holds the whole governor together, takes the tension from the belt and has all the moving parts rotating around it.

I made 2 more yesterday in steel , tried boring first and tried threading first , Both ended up being bent , I did what I normally do when things arnt working , which is to abandon it for the day, I will try again today , by holding in a collet in case its a problem with the chuck Seems to go wrong when wining the die off , new ish HHS die , See how it goes today !!

Although I've never made a governor I'm fairly sure from the photo that one would push my skills to the limit. However, as threading an un-bored 3/16" brass rod shouldn't be outrageously difficult, something must be wrong.

I suspect the die. I think it's blunt, especially as it's 'newish' and has been used on steel. I find brass cuts best with a very sharp tool and that using a drill, tap or die on steel takes enough of the edge off to make a noticeable difference when next used on brass. I try to keep a separate set of tools for brass. When they struggle to cut brass cleanly, slightly blunt tools will still work well on steel, so they're not wasted.

It may be folklore, but I believe Carbon Steel dies are often sharper than HSS. HSS's other virtues, like staying hard at red heat, may be wasted when threading brass by hand. Some chaps like to buy expensive tools and expect them to last forever. As I don't think this is always smart, I'd try a brand-new Carbon Steel die, and only use it on Brass thereafter. I see Tracy sell 3/16" 40tpi dies for £3 each. See as a disposable, like sand-paper.

Dave

I made a good one in steel this morning , holding it in a collet and putting a piece of 1/8 rod up it before threading , as suggested , I might try a brass one using that system and a new die , Thanks for the support , good to know that I am not the only one that has problems !!!

Regards

Why not screwcut it almost to size and then use the die to finish to size.

I wonder if you may have concentricity errors or uneven cutting loads which will have essentially the same effect.

That thin wall is weak and any eccentricity of loading will severely stress it. Normal dies don't need to be made to high standards of concentricity between body and thread. Obviously they will be close as any great error makes manufacture harder but trying for dead nuts is wasted (expensive) effort for all normal uses. Tailstock die holders won't be perfect either.

So there is almost certainly going to be some sort of error in alignment between die and work.

Almost certainly the error will be less than the inevitable float and clearances in the die holder system so, if the part is sufficiently strong, the die will be drawn into alignment as it cuts. The part will bend a touch to take up the load but normally that's of no consequence. However a sufficiently weak part won't be strong enough to draw things into alignment and will break, tear or distort.

Supporting the hollow, thin wall, part with a decently fitted rod up the middle makes it much stiffer and therefore able to cope with deflection loads.

Clive