Quote:
Originally Posted by thinker&planner
We use almost the exact same one. It works, but there is no easy way to make sure the broach is completely centered.
Also, it takes like 10,000 cycles of the hand lever to broach one thing. It gets very annoying, and takes us way too long. Does anyone else have experience with this, and do you have a good technique?
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We used this a lot last year to broach steel worm gears from 1/2 round to 1/2 hex. We also made some metal hex spacers out of .750 OD .125 wall aluminum tubing. It is a slow, but consistent process. If you buy some simple
wood shims from Home Depot you can remove the lateral slop from the carriage (two per side, pushed together til the carriage is snug). The shims slide fine on the painted truss. Make sure your hole is really 0.500 or more (the aluminum tubing was often a little undersize). You do not want to break a $200+ broach. Lubricate the part and the broach generously with cutting oil (coat all the surfaces, does not need to be dripping) (small paintbrush works well). Place the round end of the broach into the hole. it will be greasy so keep paper towels handy and use gloves. Setup the movable base height so that the part with broach set inside will fit (use the highest setting that allows the part/broach to fit). Start pumping the bottle jack slowly. I do not recommend an external pump - do it by hand so you can feel how much force you are putting in. You can feel if it is binding and back off. Again, you do not want to break an expensive tool (especially not in a part) so go slow and if it seems wrong, stop, release pressure and start again. You do not want to constrain the broach laterally with a setup this sloppy. Make sure your part is mounted as normal to the bottle jack as possible. The steel plates that come with the unit are level enough, but if you need to hold really small diameter parts, get 2-3 high strength 5/8 washers and stack them on the steel plates. You do not want to constrain the broach laterally - let it move so that it is normal to the part. As long as you have a good 0.500 hole the broach will guide itself just fine. You want to push down on it, but not laterally, with consistent force. Once started it will flow pretty easily and you will be pumping the bottle jack a lot (tiring). I usually use only half of the two-piece handle to reduce arm fatigue. Apply a little more cutting oil as you go, you will notice a nice little pool form where the tool meets the top of the part. At about half way the bottle jack will run out of travel. Release pressure all the way and retract the jack (may take some help if the wood shims are tight). Move the base down one setting (best done with 2 people - one lifting the base/work and the other moving the support pins for you). Check that the broach is still lubed and finish. Make sure to have someone or something to catch the broach so you do not shatter it on the shop floor! Sometime you get the tool to flush with the part top and the broach has not dropped out. Release the jack a small amount and use a 1/2 inch diameter bolt to push the broach a little farther until it drops free. Wipe off parts and you have a beautifully broached part! Make sure to also clean the chips out of the broach.
Go slow and make sure it feels right! Don't break your broach! I have had a few parts where the broach started walking laterally like crazy and backed off soon enough to save the part and the broach (was not enough lube and it was dragging weird). The broach follows your pilot bore hole, so make sure you have a properly sized (just over .500), straight bore hole for the broach to follow. I recommended experienced mentors do this the first few times because of the cost of the broach, then train students to do it with supervision.
We pressed solid aluminum blocks into Vex tubing, drilled and broached them (tubes clamped together to allow a common hex axle). We also broached a ton of .750 OD .125 wall aluminum tube into spacers. Finally we broached about ten different steel
worm gears for our tote lift gearbox.
Yes, this method is labor intensive, but allows use of a
cheap press. For the press and broach you are looking at about $400. We got our broach from McMaster, but AndyMark has them too.
If I have time I will shoot a short video.
PM me for more details.
-matto-