D shaped bore in timing pulley 1

[GAKII]

I am using a D shaped motor shaft with a standard round bore 10 tooth XL timimng pulley with a single set screw. We are having an issue with assemblers not aligning the set screw with the flat. I want to use a D shaped pulley bore, but cannot seem to find any thing of the sort. Are they possible to purchase off the shelf, or am I looking at broaching my own. Is there a special name for the bore shape? Any info is welcome.

 

[diskullman]

I think you are asking for troubleand a lot of extra expense. Train your assemblers, or run the set screw out a thread or 2 so they must assemble with the screw over the flat.

Russell Giuliano

 

[hydtools]

Use a split hub style pulley then you eliminate alignment problem.

http://sdp-si.com/web/html/newprdfairloc4.htm

Ted

 

[Compositepro]

The "D" shape you refer to is simply a round shaft with a flat machined in it for a set screw to seat. It will not work well for accurately positioning a timing pulley. It is designed for low torque and low cost not accuracy. Even if you had a D shaped hub how would that help unless it was a press fit? Any clearance will still allow errors.

 

[GAKII]

All good suggestions. The app is a low torque low low cost. I have considered a fairloc, but cost is an issue. My thinking was that if the set screw is aligned with the flat of the pulley, then problem solved, you wouldn't be able to get the pulley on the shaft without flat to flat lining up. I like the idea of running the threads out by a thread or two, but again I am relying on someone doing what they should be doing in the first place. I was looking for Poke-Yoke solution. Thanks for the help.

 

[mfgenggear]

The D shape acts as a driver , adding a set screw is used to secure it. "Right" the D is not normally use for alignment but it can be use if precision is not required.
a Keyway would be easier & more precise.
but since the motor manufacture has machine a flat on the shank! this is what your stuck with, unless they can supply a motor with shank that has a keyway.

if assembled properly the flat can be used by using a setscrew. however from my practical experience it's not best method.

if you have the manufacture supply a pully with the exact mating configuration of the D this would work! and would only install one way. full proof. a set screw would be require just so it can not slip off.

my 2 cents

 

[SincoTC]

as Compositepro stated, the flat on the shaft isn't intended for positioning or accuracy. As well as giving a decent seat for the set screw, which will help prevent slipping, it will prevent it from raising a burr on the mating surface of the close fitting shaft, which can make it very difficult to remove the pulley, especially one with an alloy hub.

Rather than try and produce an accurate D shaped hole, you could just make another plain hole in the same axial alignment as the setscrew and loctite a plain pin into this so that it protrudes into the bore and nearly reaches the flat. Your assemblers would have to line it up over the flat in order to get the pulley on.

 

[mfgenggear]

there would be added cost for handling & machining,
buying a pin & loctite, assembling and so on.

That would be all right if it is a small lot.

For the manufacture of a D hole by broaching is fast & cheap,and it's precise.. The manufacture of the pully should be able to do this if the quantity is high enough.
The quantity has to be High because of the cost of the broach & fixturing. I say ask for a quote!
It will not hurt to ask.

I have keyways & D holes broach for my customers gears all the time. a pulley would be easy.

 

[eromlignod]

Sounds like you need to administer regular beatings to your assemblers.

Don
Kansas City

 

[MikeHalloran]

The guys who mold timing belt pulleys out of plastic have cleverly designed their molds so that custom bores, e.g. D-shape or whatever, can be produced with relatively inexpensive tooling inserts.

You may find someone already tooled up for the exact bore you need.

If you must pay a tooling fee for a mold insert, take the time to also build in a retaining feature, e.g. a depressed finger to provide friction, and a lead-in taper so that your assemblers can just roughly align the bore with the shaft, and finish the assembly with a hammer blow.



Mike Halloran
Pembroke Pines, FL, USA

 

[drawoh]

GAKII,

Could you cut a keyway in your pulley such that a shaft key would pick up the shaft flat? This would involve a more standard fabrication process.

I hate set screws. They dig into your shaft taking the screw and shaft up past their elastic limits, then they deform further as the system stop and starts, or reverses itself. For anything more complicated than a fan pulley, I recommend split hubs, as noted above.

JHG

 

[plasgears]

We had particular success with a self broaching design.

The hub should be hardened PM, a relatively economical approach. The shaft is softer, and at assy, press the hub onto the shaft. No pin required; no clearance.

The application was an ice crusher actuator, 150 in-lb on a 3/8"D shaft. The output gear was HT PM with a splined bore shape. The shaft was stepped to meet the spline at pressing.