# Key way broaches and sizes



## Metal Butcher (Dec 27, 2010)

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


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## doc1955 (Dec 27, 2010)

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


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## PaulG (Dec 27, 2010)

$78 for the set.

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


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## GailInNM (Dec 27, 2010)

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


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## Jasonb (Dec 27, 2010)

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


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## kvom (Dec 27, 2010)

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


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## Metal Butcher (Dec 27, 2010)

Jasonb  said:
			
		

> 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


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## Jasonb (Dec 27, 2010)

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


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## MachineTom (Dec 27, 2010)

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.


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## Metal Butcher (Dec 27, 2010)

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


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## Jasonb (Dec 27, 2010)

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

Jason


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## Metal Butcher (Dec 27, 2010)

Jasonb  said:
			
		

> 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


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## Metal Butcher (Dec 28, 2010)

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


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## jpeter (Dec 28, 2010)

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.


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## hammers-n-nails (Dec 28, 2010)

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.


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## Metal Butcher (Dec 28, 2010)

hammers-n-nails  said:
			
		

> 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


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## GailInNM (Dec 28, 2010)

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


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## Metal Butcher (Dec 28, 2010)

GailInNM  said:
			
		

> 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


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## GailInNM (Dec 28, 2010)

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


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## Metal Butcher (Dec 28, 2010)

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


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## Jasonb (Dec 29, 2010)

MB I've done plenty of keyways using the lathe carrage, your biggest problem will be the small size of the bore as the absolute max tool holder you could use is going to be 9/32" to allow 1/32 tool projection. This will tend to flex alay from teh cut quite a lot but with patience and 0.001 depth of cut you can do it

Your 9x20 will be upto it I did most of mine on an 8x24 Emco which the imports are copied from, this is a steel gear centre, four 3/16" keyways 1" long and I don't have spindle lock. 

The shaft keyway is easily done with an endmill or slotdrill, this is the matching shaft with keysteel soldered in to form a splined shaft.

For a small 1/16" keyway you could well be able to press it in using a bench drill though I would not use it on anything over 1/8 as it could strain the rack. I have seen larger ones done by puting the flywheel over the edge of a bridgeport table and raising teh table onto the broach pressing under the arm.

Another option that would work is to bore the flywheel oversize by 1/16, turn up a sleeve to fit the flywheel and shaft then cut a 1/16 slot down the sleeve. This can now be silver brazed into the bronze flywheels or locktite into the iron ones. The Minnie traction engine in my avitar uses this method on 9/32" shafts.

J


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## arnoldb (Dec 29, 2010)

Just a thought...

Could you pre-drill the area where you want to broach the keyway in the flywheel with a 1/16th (or slightly smaller) drill ? - That will leave less material to remove while broaching.

Regards, Arnold


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## Maryak (Dec 29, 2010)

To expand on Arnold's comment-Why not use a round key and drill/endmill/ream the shaft and flywheel together. ???

Hope this helps

Best Regards
Bob


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## Metal Butcher (Dec 29, 2010)

Thanks Jason,Arnold, and Bob for even more good ideas of ways to secure my flywheels. 

Plan A: I was trying to get the winning bid on a set of Dunmor broaches that the E-bay seller claimed was new, but based on the pictures shown, and looking them over, and over, I started to have some reservations, and stopped my biding way short of the $110. winning bid.

http://cgi.ebay.com/ws/eBayISAPI.dl...2F6QLjw%3D&viewitem=&sspagename=STRK:MEWAX:IT

Plan B: After wards I made the decision and purchased the same Dunmor Minute Man KSB-08, #00 size boxed set of broaches and bushings from Amazon, new w/warranty for $20 more. There were 2-left when I made the purchase, and when I refreshed the page it showed only one left and the price went up by $22. What was that all about?

I was thinking of getting the lower priced import set (about $90 w/ship) that I'm sure would have been more than adequate, but "Honey" got involved and insisted by saying, "I don't want to hear about how you would fire the person responsible at the factory that made them!" With the current economic situation this country is in, I feel that I just made a small donation towards our economic recovery.

Honey knows that I can be critical at times, so what could I say? ;D

-MB


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## Metal Butcher (Dec 29, 2010)

I forgot to ask you to take a good hard look at the pictures in the E-bay link I provided.

On the out side of the box it looks like half the factory label has been cut away. There are two added pieces of tape with some sort of numbering or lettering that doesn't belong. And it looks like all that's left of the latch is the pin. I know the outside doesn't really matte,r but the listing says "brand new".

On the inside the bushings don't have a new consistent look about them. Only one of the broaches, the one in the middle is in a red capped container. There also some pieces that appears to be key stock in the upper part of the box. Both pictures are out of focus, with over 600 feed back you would think this seller would have learned how to take a focused picture. For something that's claimed to be "brand new" and never been used, this all looks a little fishy to me.

http://cgi.ebay.com/ws/eBayISAPI.dl...2F6QLjw%3D&viewitem=&sspagename=STRK:MEWAX:IT

Maybe I'm wrong. What's your opinion?

-MB


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## MachineTom (Dec 29, 2010)

I've a set of Dumont broaches but the smallest A size broach I have is 1/8 keyway. It is very simple to make a bushing to fit the broach and with 10 to do don't fool around with the lathe, or mill, buy a broach. (I'll lend you the 1/8 if you would like). An A broach needs a groove milled into the bushing of .205"d x .128"w regardless of the keyway width, The bushing should be the lenght of the keyway to be cut or more. The max lenght of cut is 1.125 you can stretch this some with cast iron, 25% of so.

The broach will fit about 1/2-3/4" into the flywheel before the cutting, it begins to get stiff at around 1" in depth. A trick to avoid bending a broach, is to push 1/2" in, then release pressure, press another 1/2" repeat, this will take care of slight alignment issues as you push the broach.


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## Metal Butcher (Dec 29, 2010)

MachineTom  said:
			
		

> I've a set of Dumont broaches but the smallest A size broach I have is 1/8 keyway. It is very simple to make a bushing to fit the broach and with 10 to do don't fool around with the lathe, or mill, buy a broach. (I'll lend you the 1/8 if you would like). An A broach needs a groove milled into the bushing of .205"d x .128"w regardless of the keyway width, The bushing should be the lenght of the keyway to be cut or more. The max lenght of cut is 1.125 you can stretch this some with cast iron, 25% of so.



Hi Tom. Thank you for your generous offer to lend me your broach. Yesterday I ordered a #00 Dumont set . Its the small precision set that cut's 1/16", 3/32", and 1/8" key ways. This set will cover my immediate needs, and hopefully all my future needs for building small engines.

-MB


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