Key way broaches and sizes

[Metal Butcher]

I need to make a decision soon as to whether I should use set screw, or keys to secure the flywheels on my current Upshur engine's project. The crank shafts are 5/16" (.312"), so what would be the correct size key that should be used?

If I decide to go with cut key ways in the flywheel bores, has anyone had experience with this brand of import broaches? Or any other brand?

http://www.shars.com/product_categories/view/2030201/HSS_Standard_Keyway_Broaches_with_Shims

-MB

 

[doc1955]

Here is some good reference material on key ways.
Key ways

 

[PaulG]

$78 for the set.

http://www.shars.com/products/view/4997/No_00_Precision_Keyway_Broach_Set

 

[GailInNM]

Generally the key way width is 20% to 25% of the diameter of the bore. I would use a 1/16 key way. It is on the low end of the width, but for light duty use on a model engine it would be OK. Just keep the key a close fit.

I have a Dumont 00 set which is what the Shar's link pointed to by PaulG is a copy of. I bnought mine many years ago and will never wear it out building models. I would not be afraid of the Shar's boraches for model work as I have had good success with their products overall. It won't be the quality of the Dumont, but it will probably out last your model building lifetime in a home shop.

Gail in NM

 

[Jasonb]

I would also go with 1/16 on that size of shaft, It may be worth still having a set screw that bears on the key just incase your tapered key won't hold.

I usually do them by planing on the lathe but having seen that set think its time to get my wallet out. We can get cheaper imported sets over here but they don't go that small.

Jason

 

[kvom]

For small models like this I believe 609 or 620 Loctite will hold just as well as either setscrew or key.

 

[Metal Butcher]

I would also go with 1/16 on that size of shaft, It may be worth still having a set screw that bears on the key just incase your tapered key won't hold.

I usually do them by planing on the lathe but having seen that set think its time to get my wallet out. We can get cheaper imported sets over here but they don't go that small.

Jason

Hi Jason. I plan on using a set screw to hold the key, if I decide go with a keyed flywheel and shaft. I thought the set screw was an absolute necessity.

"Tapered key"? Newer saw one of those , and I don't think that I have any in my assorted box of keys. Guess that would eliminate the need for a set screw. I'll have to look into those. Would making minor positioning adjustments or taking the flywheels off be a bit tricky.

-MB

 

[Jasonb]

Commonly known as a gib key here, they have a "L" shaped end which allows a wedge to be used to extract them or on larger sizes a jacking screw or the thread can be used to take a slide hammer. My traction engine has this type of key, the taper is very slight and holds well.

Jason

EDIT some details of tapered keys here they are covered by a British Standard

 

[MachineTom]

Another way to fix the flywheel to the shaft is with a tapered pin. They come from 6/0 which has a large end dia of .078", a pilot hole and a pin reamer and the job is quick and can be removed when needed.

 

[Metal Butcher]

I'm on a hunt for key stock since my assortment box doesn't have anything under a 1/4".

So far the smallest gib keys (tapered) that I found is 3/16".

Parts catalog, page 27. http://www.hitnmiss.com/index1.html

Regular key stock is common in 1/16".

http://www.drillspot.com/products/388057/Approved_Vendor_5UY15_Key_Stock?s=1

-MB

 

[Jasonb]

I've made them out of Gauge plate (Ground Flat Stock) in the past, no need to harden them though.

Jason

 

[Metal Butcher]

I've made them out of Gauge plate (Ground Flat Stock) in the past, no need to harden them though.

Jason

Jason, Making them would be the only way to go. The few sites that have them, show a price of around $5 to $6 apiece ! Yikes!
I would have to spend about $50 to $60 plus shipping. With standard key stock in the smaller sizes running around $2 a foot, I might be better of with that as an upgrade, from the indicated set screws on the plans. I could defiantly see buying or making them for an engineered scale model.

-MB

 

[Metal Butcher]

Hi guys,Thanks for all of your input, and suggestions of the alternative methods I could use to secure the flywheels on my build projects.

I Think that using the 1/16" key ways might be my best option. Certainly not the simplest method as some of you ideas point out. But I need the ability to shift and and position the flywheel to adjust the governor assembly, and also the other flywheel to adjust the hall sensor set up. Its also important that the flywheels be removable without any fuss.

Using the key way's presents altogether new problems for me. How do I slot the small already assembled crank shafts. A slitting saw won't have enough clearance, even if I could come up with a way to set up the cranks for cutting the key ways. And how do I push the broach through to cut the key ways on the flywheels. All I have is a small 1/2 ton arbor press that apparently doesn't have enough clearance for the 5" broach, plus the flywheel, assuming that this is the only correct way. The throat clearance on my press is only 4-1/2".

-MB

 

[jpeter]

Keep a good fit or else it'll knock. You'll probably have to locktite it to keep it from knocking. The taper works best like a taper on the shaft and a matching tapered bore in the flywheel. If you setscrew it on without the key file a flat on the shaft for the setscrew. If you don't the setscrew burr will prevent you from getting the FW off. I'd suggest because it's done, file a flat for the setscrew, add locktite, and screw it on.

 

[hammers-n-nails]

you can push the broach through with the tailstock on your lathe if it can take it. my grandpa says they used to cut internal keyways by grinding a boring bar the right size and running the carrage back and forth instead of using a broach, similar to a shaper, i guess you could do something similar for the shaft, ive never tried it.

 

[Metal Butcher]

you can push the broach through with the tailstock on your lathe if it can take it. my grandpa says they used to cut internal keyways by grinding a boring bar the right size and running the carrage back and forth instead of using a broach, similar to a shaper, i guess you could do something similar for the shaft, ive never tried it.

I have seen key ways cut in flywheels with a square tool bit, with carriage movement. I'm surprised no one else brought it up. If I could lock my lathe spindle I would try it for sure. And, without much leverage available from my 9 x 20 lathe carriage hand wheel, a few thousands per cut might be all that I could muster. I'm Not sure how the crank shafts should be done. Maybe if I clamp the shaft in the milling vise a 1/16" end mill would work, or maybe not, it might be too much of a cutting load and I wonder if it would cut oversize?

With 10 flywheels needing a key way cut, an overpriced broach is looking mighty fine right about now.

Edit: Not only is my spelling way off today, I forgot to answer you on your great suggestion. Yes, I think the tail stock might have enough oomph to push a small 1/16" broach.

-MB

 

[GailInNM]

MB,
If you start it with the tail stock you could finish it with your arbor press after the broach was in far enough to fit under the arbor ram. When the broach is starting to cut it does not take too much pressure as it is just cutting on the corners, but when the fulll width of the flat starts cutting the pressure goes up considerably.
Gail in NM

 

[Metal Butcher]

MB,
If you start it with the tail stock you could finish it with your arbor press after the broach was in far enough to fit under the arbor ram. When the broach is starting to cut it does not take too much pressure as it is just cutting on the corners, but when the fulll width of the flat starts cutting the pressure goes up considerably.
Gail in NM

Thanks Gail, that's a great idea!

Will my 1/2 ton be enough though? Its be falling a little short on most pressing occasions.

-MB

 

[GailInNM]

MB,
Your 1/2 ton should be fine. If the ram is adjustable, take out what side play and fore-aft play that you can. Side loads are broach killers. Use cutting oil.

A 1/16 end mill should work fine on the shaft. Your finished depth is only about 1/2 a cutter diameter. Keep the overhang on the end mill as small as possible. I would run the mill RPM as fast as it will go. I should not cut oversize if the feedrate is kept low. If you feed too fast the cutter will deflect in a slot an go oversize. I use carbide 1/16 regularly and most of the time the slot will be a little bit narrow and the cutter tolerance is minus a few tenths. On a manual mill I would probably make three pass, each about 0.010 deep.

I would try it out on a piece of scrap first to get a feel for it.

Gail in NM

 

[Metal Butcher]

Thanks again Gail. I'm going to re-read your posts in the morning, just to make sure I got all of it burned into my memory.

-MB