hadfield Power Reverser

[Jim_Nolan]

Right, after years of searching I have finally got a full set of Hadfield reverser drawings. The screw reverser shaft has a 3 start thread with a 2” lead and it is 1,625 O/D so that scales to about .28” dia on my locomotive.

So the big question is what thread should I be using at that diameter I am guessing a multistart thread is a possibility but is there a tap and die combination I can use as a compromise that will not end up with me winding for ever.

Jim

[FLtenwheeler]

How about Acme threads. In 1/4" you have 8, 12, 16, and 20 threads per inch.

Tim

[Fender]

I started to suggest that you make a three-start die with an OD of .28 and a lead of .345 inches, but my little grey cells shorted out....

[Fender]

OK, seriously, Tim is on the right track. Here is a multiple-start acme threaded rod from McMaster. It is .216" in diameter, 20.8 threads per inch, and four starts. So each turn of the rod moves the nut .192 inches. Said another way, it takes 5.2 turns to move the nut 1 inch:

http://www.mcmaster.com/#acme-threaded-rods/=b4yno2

I also saw a 1/4-16 acme rod with four starts (part #6350K11) that is a little closer to size, but is pricier because it comes in six foot lengths.

[FLtenwheeler]

OK, seriously, Tim is on the right track. Here is a multiple-start acme threaded rod from McMaster. It is .216" in diameter, 20.8 threads per inch, and four starts. So each turn of the rod moves the nut .192 inches. Said another way, it takes 5.2 turns to move the nut 1 inch:

http://www.mcmaster.com/#acme-threaded-rods/=b4yno2

I also saw a 1/4-16 acme rod with four starts (part #6350K11) that is a little closer to size, but is pricier because it comes in six foot lengths.

Purchase the nut and cut the 4 lead screw.

Tim

[kvom]

16TPI 4 start means each thread is 4 tpi, not easy to cut on a small lathe.

[Trainman4602]

Cutting multi lead threads is a simple thing to do on any lathe. For a three lead screw you have to make an indicator plate on the left side of the head stock around the spindle this could have three equal marks with one on the spindle. You then cut the thread by making a cut as usual then disengage the head stock gear and relocated it and the second make and then do the same for the third mark. Continue to do this until the thread is deep enough. The difficulty comes when trying to fit the nut. I have made the male part but I usually had the nut to fit up too.

All in All it’s easy but tricky but it can be done.

[Harold_V]

Cutting multi lead threads is a simple thing to do on any lathe. For a three lead screw you have to make an indicator plate on the left side of the head stock around the spindle this could have three equal marks with one on the spindle. You then cut the thread by making a cut as usual then disengage the head stock gear and relocated it and the second make and then do the same for the third mark. Continue to do this until the thread is deep enough. The difficulty comes when trying to fit the nut. I have made the male part but I usually had the nut to fit up too.

All in All it’s easy but tricky but it can be done.

Alternately, the thread can be cut between centers, using the jaws of a three jaw to drive the dog tail, thus indexing the part. Slow, but effective. Same problem with fitting----it's not convenient.

Harold

[kvom]

My comment was that a .25" pitch can put a strain on a small lathe's gear train. If there's enough HP then, as posted above, the technique is simple enough.

[Fender]

Also, if the threaded rod is of any length, a follower rest will be mandatory. If built to scale, the o.d. is only .280 inches. A huge amount of side relief will be needed on the tool.

[Jim_Nolan]

Thanks to Dan for doing all the brain work and to the other comments.
I pressed the buy button on McMaster Car but they declined my order.

Hmm., my credit rating must have gone further than I thought.

Jim

[Chris Hollands]

Jim , Im looking at building an Australian Loco in the future and it has a Hadfield power reverse ,is there any chance to get a copy of the info you have.
I will pay what ever costs are involved.
Thanks Chris