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View Full Version : broaching without a machine???



Tony
02-23-2003, 07:54 AM
as it happens every now and again i'm asked
to cut keyways into gears or pulleys etc...
internal broaching.. and i always have to turn it down as i dont have the (proper) equipment
to do the broaching.

out of curiosity i'm wondering if anyone out there has "cheated in" a few internal keyways. nothing too deep/long, say a .5" thick gear needs a keyway cut.

i've got the usual host of equipment: lathe, mill, drill press, HACKSAW, etc... any tools out there i can adapt to do some broaching??

i can't justify buying a broaching set, especially since i have no ideas what range/sizes might come in the door.

thanks,
-knucklhead

SGW
02-23-2003, 08:27 AM
Sure....it's quite do-able. You can make a chisel-shaped (for lack of a better description) cutter out of a piece of drill rod, put it in your milling spindle, and shave out a keyway by racking the quill up and down by hand.
You can do the same kind of thing in a lathe, by putting a cutter in the toolpost and racking the saddle back and forth.

There's obviously a limit to the size keyway you can do this way, but 1/16" is pretty easy. I suppose you could even do big keyways if you had enough patience. You couldn't do the entire width in one pass though.

The topic of keyways came up a while ago, and there was some discussion of alternatives, like drilling a longitudinal hole on the shaft/gear parting line and driving in a pin so half the diameter (more or less) was in the shaft and half in the gear.

You can also file a keyway fairly successfully, if you have a good selection of small files. In that case, it may help to use an end mill of the proper diameter to mill as much of the keyway as you can, then just file out the corners. Trouble is, keyways typically aren't much deeper than they are wide, so you can't get very deep with an end mill.

JCHannum
02-23-2003, 08:50 AM
Another method is to make a one tooth broach.
Take a piece of shaft the diameter of the hole, and mill a slot the length and depth of a HSS lathe bit ie: 1/8 x 2-1/2". Drill and tap a hole in the "front" of the slot for a small set screw say 5-40. Install the setscrew from the backside to jack the cutter out a bit at a time, and using cutting oil, press the broach through in multiple passes, moving the cutter out a couple thousandths each pass. You can mike over the shaft and cutter to determine final depth.
You should grind the rear of the cutter to fit the radius of the slot, and probably about a 5* land on the front would be appropriate. Leave the slot long in front for room for chips.

happy02
02-23-2003, 08:50 AM
SGW is correct, you can broach by shaving in a mill or lathe. I've done both. I make a boring bar out of crs just smaller than the hole id. Mill a slot in the end of your bar the size of the tool bit you'll be using. Silver solder a plug on the end of the bar to cover the slot and drill & tap a set screw in it to lock your tool bit. Then cut a tool bit the width of the bar and grind the end with a small amount of back rake and just a little side rake too. If you forget the side rake you'll chip the bit. Mount the gear to be broached in the mill and center your bars cutter on it. Lock the quill so that it cannot turn and start taking small cuts by raising and lowering the spindle till you've reached half depth and your thru. It's really harder to splain than to do.

wierdscience
02-23-2003, 10:58 AM
You can also buy a proper keyway broach and make your own bushings and shims for it.

WJHartson
02-23-2003, 03:20 PM
I have made an attachment for my arbor press that allows me to broach in it. I use if mostly to make square hole out of round ones. Have done keyways in the lathe as dicussed in other posts. If you want I can e-mail you pictures of the attachment. I don't have a way to post pictures on the net.

Joe

Al Messer
02-23-2003, 03:50 PM
Anybody besides me remember the tool called a "file"?

yf
02-23-2003, 04:17 PM
Iv'e cut some keyways, internal and external, by chipping with a cape chisel and filing to size.

Needless to say I don't look forward to doing it that way ever again.

If you need to fix a wheel near the end of a shaft the easiest way to key it is to drill axially at the intersection of the shaft and bore and insert a round key as described in the posts above.
Drilling in this way is also a start to fileing a square keyseat.

When I used to service overhead doors, I would sometimes just drill a crosshole in a hub and shaft and put in a bolt and nut. Crude but very effective. Never had a call back on a job like that.
Keys loosening and falling out are a big problem there, as if a key falls out and the spring is weak or broken the curtain falls down. Iv'e had several close calls that way.
The faster those roll ups come down the less noise they make. http://bbs.homeshopmachinist.net//biggrin.gif

Rich Carlstedt
02-24-2003, 01:38 AM
Special broaching in the BridgePort
Not to hard at all !

I do it Because I don't have a broach set

Step one, take a broken (or old)2 flute tap and grind one side of it to the width of the keyway ,removing all the threads so that you have a broach on one side. Put about a 7 degree rake on the nose. A tap is used, since it fits nicely in a R8 collet. Mike the sides of the "broach" and hold parallel with maybe a .001 taper inward to the shank.
This will give some clearance, but not allow the tap "Excuse Me" broach to drift.
Now mill the keyway half round with an endmill removing most of the metal.
Mount the broach, lock the spindle from turning, and manually broach the keyway with the quill feed, feeding in .001 thousandth at a time (with the table) till you go in as far as the endmill raidius point at the center.
easy ??

I have also made my own broaches (like a .078" width) by taking a broken endmill (no flutes) and chucking it in the lathe. Run up the speed as fast as possible (1400+) and drill into the shank with a carbide drill to make a Broach holder (drilled .125 on above unit about 1/2 deep)) took a piece of tool steel . 078 thick X .090 X 1" long and pressed it into the endmill shank hole.
Touched it up on the grinder and I had a special broach that fits my R8 collets.


While I did grind the .078 thickness on a (school) surface grinder, most of my grinding is off hand.
You may want to buy HS Toolbits (1/8 X 1/8, or 1/4 X 1/4 etc) and insert them in old mill shanks for a quick way of making broaches

Rich Carlstedt
02-24-2003, 01:46 AM
Forgot to say that drilling out old broken (no flutes) endmill shanks is easy for you newbies out there. Carbide drills are fairly cheap and the secret is to get the metal "Hot" and keep it that way. when you start drilling the part turns red....Good.. keep feeding in hard till you are 1/2" deep or so, and get out fast. When you stop feeding , the part cools and shrinks on your drill...sometimes breaking it
Remember if a part "screams' at you it means you are not feeding fast enough !!!

Herb Helbig
02-24-2003, 10:03 AM
Rich -

I noticed that your home made broach with 0.078 x 0.090 (0.119 diagonal) tool pressed into a 0.125 hole seems loose. Does the 1/8" hole shrink that much from having been drilled red hot?

And thanks for the carbide drilling tips!

C. Tate
02-24-2003, 10:39 AM
If you got time to file a keyway then you probably do not charge enough for your work. You can buy a 1/4 broach from MSC for $25.00 and use the lathe or mill to push the broach throught the part.

lynnl
02-24-2003, 11:47 AM
Question: How do you lock the spindle on a Bridgeport? (Yep, I'm a novice!) I see that mentioned regularly, and have wondered about it before. Is this referring to the little lock up by the drawbar that when pushed to either side permits loosing/tightenng the drawbar? I've never thought that to be a very tight (or maybe dependable) grip... am I wrong?

JoelK
02-24-2003, 08:47 PM
I recently did one with a file, but considered doing the following: Make up a powered hacksaw type device or jigsaw, but put several hacksaw blades side by side. Adding or subtracting blades would allow different sized slots. Problem would be, getting correct width out of a combination of blades.

Anyone ever try this?

wierdscience
02-24-2003, 08:51 PM
If you have an eight speed head you can drop it into high gear and flip the backgear lever into low or vice versa and lock the spindle.If you might need to do this on a regular basis I would recomend making a lock that clamps to the quill and tightens on to the spindle.There is one advantage to using the mill to broach with as you can do things you would never attempt under power.One time I had to make an 8mm internal keyway that stopped against a shoulder I used a narrow woodruff cutter to cut an end relief for the chips the keyway was about 2"long and believe it or not I did it in about fifteen minutes once I had the setup.

JCHannum
02-24-2003, 10:11 PM
Weirdscience says he did it in about 15 minutes once he had the setup. How many times have you guys spent 4 or 5 hours preparing a set up that took 2 minutes to do?
Whenever anyone asks me what I am doing, I am usually making something to make something.

Rich Carlstedt
02-25-2003, 12:26 AM
Herb
getting sloppy with writers "allowences"
The carbide drill was actually a 3MM drill (surplus sales pickup) and the part was .09 or over slightly....It was a nice light press fit(actually broches itself in)

The shank does shrink somewhat, and gives a tapered hole ! probably .001 to .002 smaller at the bottom. Depends on force of carbide drill and hole size.

Lynn
Yes,the handle you mentioned is the spindle brake, which works when pushed or pulled, however (By Design !) if you pull it out after push/pull, it will stay in position thereby locking the spindle, until you hit it again, which releases it.