[peter.blais]

Hello guys.

I'm working on a part which has a male keyway inside a small bore. The factory piece is sintered iron and they just press it together- easy. Machining that though- not so easy.



Here's what I mean-

Anyways, I was thinking about using a rotary broach to do this in process in the cnc mill / lathe. It's either that, or use a standard broach I suppose.

Anybody ever seen anything available off the shelf to make something like that? If not, any clue on where I should start the search?

Thanks,

Pete

[307startup]

That's easy...broach your keyway undersize or use an oversize piece of keystock, and pressfit it afterwards.

Imitate the bigboys...they got their stuff figured out

[Medm]

Having access to EDM machines, this is the way that I would add that feature to the part in question.

This is a very easy task for an EDM machine, you just need to add a hole in the center of the part if you don't have an initial hole unit.

If you don't have access to an EDM machine, it could be accomplished using a combination of drilling and milling. Using 1/16th of an inch drill in the corners where the key meets the major ID and an appropriate drill for the center, you could then mill the rest of the feature out to suit.

I hope this helps...

[307startup]

It's a freakin' aluminum adjustable timing pulley for an engine, not a component for a space shuttle! Don't overthink it. Cut the part on a lathe, broach the keyway undersize, pressfit (with epoxy) an appropriate size piece of keystock in there.

Trust me, that's what the big dogs do...even the aftermarket companies. Ask me how I know?

[peter.blais]

I've seen these both one piece and with a loose keyway. I'd much rather go with a 1 piece setup.

I'm not making like 2 of these- rather hundreds- and the tool(s) would work for multiple applications as well. So, I wouldn't mind spending a bit up front to make it happen.

I'm already stuck needing a cutter for the tooth on the outside, as it's a funky trapezoidal tooth form from the 80's.

[307startup]

Rotary broaches induce a twist on the finished product...the spline or male keyway will literally have a faint twist on the Z axis...the longer the spline/male keyway, the more severe this twist is. So that's out if you want them to actually engage the cams properly. Not to mention a rotary broach won't produce a single male keyway, due to the rocking motion that creates the cutting action. You could hydraulicly broach them...just ONE broach will run you $4000...and you'll still need a hydraulic bench to pull the broach with, plus the setup fixture. Figure $5000 for a properly set up hydraulic system, one with adequate power, safety mechanisms and control components, $2000 for the material to build the bench, and another $1000 for an in-house built fixture to locate the workpiece precisely and repeatedly.

EDM for this application is overkill and way expensive. I don't know anybody who would buy a set of these for $1000+...which is what your markup would have to be to cover the cost of EDM'ing these.

If you don't have a shaper, you can always use your VMC as one, though the same issue of twist arises, even with a locked spindle...

You want to know how that male key arrives there in the one-piece deal? It's a custom aluminum extrusion that is finish machined on the bore. Got a spare $10-20-30,000 laying around? Because that's what the die and the first 1000 lbs of extruding will cost you. And that's WITHOUT material costs. Unless you have an extruder in your back pocket, there are no sweetheart deals, that's an industry standard...unless you're willing to sign a contract for 10,000lbs of extrusions, then they'll throw the die in free. Hmmm...let's see here, 6061 is around $4.50/lb right now, if you can find a supplier who isn't backlogged or cut production...that's $45,000 just for material, minus setup fees, extrusion costs, scrappage, shipping...and you said you were wanting to make hundreds...not thousands or tens of thousands. Figure an average blank thickness of 1.5" after sawcutting, per 20 ft. bar you're looking at 160 pcs, and that bar will weigh about 80 lbs if it's 3" OD with a hole through the middle. You're 8% of the way through utilizing your $20-30,000 investment for the die and extrusion contract at 1000lbs....

Like I said before...make it easy on yourself. You can knock these out on the lathe quick as you can load material, broach them, and build a two-piece tool to set the key for far less than you could do them anyother way. And they'll work just as well. Powdercoat them instead of anodize and nobody will be the wiser. All you need is a lathe, a couple of tool holders, a package of inserts, an arbor press, an abrasive cut off saw to cut the keystock, a grinder or belt sander to dress the cutoff keystock and the material for your pulleys.

As for the tooth form on the pulley, it's not an odd 80s trapezoidal form. It's a special form that applies to toothed/ribbed belts. The tooling is already made for them, how do you think the manufacturer that supplied the automaker made them? You just have to have patience and figure out the tooling vendor in order to purchase the appropriate form tool.

I could suggest all sorts of high-tech, but totally worthless ways to make this part. Nano-tech...we'll build it up one angstrom at a time! OR how about laser sintered parts? OR we could use chemical ablation! Or, or, or...you could listen to reason and manufacture it the EASY, PROVEN way.

You can lead a horse to water, but you can't make him think

I've seen these both one piece and with a loose keyway. I'd much rather go with a 1 piece setup.

I'm not making like 2 of these- rather hundreds- and the tool(s) would work for multiple applications as well. So, I wouldn't mind spending a bit up front to make it happen.

I'm already stuck needing a cutter for the tooth on the outside, as it's a funky trapezoidal tooth form from the 80's.

[peter.blais]

Ya, its curvilinear II-

Anyways, I see what you are saying about rotary broaching- yes, EDM is way too slow, so are 1/16" drill bits and tiny end mills.

Not sure that it wouldn't engage just fine with rotary broaching though- the keyway is only 3/8" long. You'd have to have some serious twist to have it not fit. I definitely have had ones on my desk before as well which are most definitely made from one piece- anodized and not powder.

I might call those guys tomorrow and inquire.

[307startup]

My experience with the keyways in cams are that they are pretty high-tolerance...and they have to be if you don't want your timing slipping by a few degrees forward and back everytime you get on and off the throttle.

Which means a few thou twist in the key is going to be a ***** to get on the cam...which means Joe Sixpack is going to reach for a hammer and pound hell out of your cam sprocket. Which isn't going to do any good to your cam sprocket, his cam, his cam bearings or his cylinder head(s). Which means an angry customer.

But it's your product...

Ya, its curvilinear II-

Anyways, I see what you are saying about rotary broaching- yes, EDM is way too slow, so are 1/16" drill bits and tiny end mills.

Not sure that it wouldn't engage just fine with rotary broaching though- the keyway is only 3/8" long. You'd have to have some serious twist to have it not fit. I definitely have had ones on my desk before as well which are most definitely made from one piece- anodized and not powder.

I might call those guys tomorrow and inquire.

[peter.blais]

The keyway on these is only for alignment / assembly. The clamp load is what holds the gear in place on these. One of the guys making these gears supplies like a 1/8" little corner of a keyway haha- they work just fine, but it does make customers nervous as hell.

They will break even the OE steel keyways if you haphazardly put in the bolt. So, an aluminum keyway will shear like nothing if the torque overwhelms the friction from clamp load.

I'm still considering a steel keyway- I could buy bars of key stock, grind the one side to get them to size- cut them into little pieces and figure out a way to debur them. I have a feeling though getting all that done and deburring them without having it look like amatuer hour- and doing it quickly- will be the trick.

Wheras, if I broach them, then anodize- it will be tidy, and possibly done all in one setup right in the machine.

I have a hard time believing the rotary broach won't be straight within a thou or two over .375"? Anybody else try one of these?

They cut splines and such with those- if you cut a deep tight fitting spline and it had much more twist then that- it's not even going to assemble.

[packrat]

These guys probably have the broach you need in stock;
The duMONT Company, LLC - Special Broaches The stock broaches really aren't that bad, price wise. It's worth a phone call or Email for a quote. You could even grind the slot/key into the correct size round broach.

The hole/key way would be the first operation to machine, then fixture from that to make sure every thing is indexed to the key. But you probably know that.

cary

[peter.blais]

Hi there.

I'll call the tomorrow. I spoke with slater today about rotary broaching, and apparently they cannot broach a single male keyway. They can do two, 180 apart- but not one- too much force on one side of the broach, or so he said.

Ya, definitely want to broach it before drilling any features w/ an angular relationship to it.

Good idea on grinding into an existing broach. I would bet they would even do that for me without spending a fortune- seems like it would be pretty quick to setup if you already had a surface grinder- unfortunately I do not.

I think I have a line on what the actual tooth form is, but will probably just farm out the outer ring- I don't have a 4th on my mill.

Thanks for the input so far guys

[icutting01]

i think you can find your perfect broach here. they have all kind of broaches and you can find what you need in a very fine price.

Keyway Broaches @ http://www.indiancuttingtools.com/broching_tools.php