Presses and techniques for 1/2" HEX broaches

[Cory]

Originally Posted by asid61

I feel like I'm missing something. What's wring with just using the 1/2" shank on the bottom of the broach to keep it straight? Is that not good enough?

All the presses I've seen that use bottle jacks have very sloppy tolerances that allow the ram to shift position laterally. It is virtually impossible to get a consistent result without constant fiddling with the broach/part, even with a fixture.

In general, if you know that whatever you're inserting the shank into is perfectly perpendicular to the table, that is a suitable means of aligning the broach.

To the earlier question in the thread, rotary broaching is viable, but it is also finnicky to get a good fit. We have been using a rotary broach for 5 or 6 years now, but almost every rotary broached part we make, we run a push broach through afterwards to eliminate the "twist" you get in the hex profile due to the way rotary broaching works. The nice thing is no alignment is necessary for this, as the existing hex guides the broach.

I would HIGHLY recommend against using anything with bearings to broach (a lathe, drill press, mill, etc). You can brinnell your spindle bearings and destroy them.

[weberr]

I have an old two column press that came out of maintenance shop from the Masonic Temple in Detroit, probably circa 1920's. Works like a charm!




http://www.practicalmachinist.com/vb/attachments/f38/112939d1406518134-large-arbor-press-arbor-press-10.jpg

[RoboChair]

Back in the day 1678 would use the knee and turret of our bridgeport to broach 1/2" hex by putting a piece of 80/20 with a central hole underneath and raising the table.

Buy yourself a properly sized arbor press(or modify the arbor on one to have a deep hole and do it in 2 stages). Thank me later.

[weberr]

Also,

Make sure you hole is true; I prefer a drill and ream to size. You must also lubricate the broach for best results. In my home shop (where the press is) I have used diesel fuel, Kerosene, WD-40, or fine spindle oil. If you slightly back off the ram before each stroke, the broach can recenter itself and stay true to the hole. If you are broaching items thinner than the distance between the teeth on the broach, use a scrap piece with the same hole size to make up the distance and keep the broach running true.

DO NOT WIRE BRUSH A BROACH AS YOU WILL DULL IT. DO NOT RUN IT IN BACKWARDS EITHER!

[mott]

We just purchased a 3 ton ratcheting arbor press off eBay for $168 (plus $98 shipping) that has sufficient stroke for our hex broach. The press isn't a Dake but should suffice for what we need to do and about 1/10th the price.

[DampRobot]

On 100 I used to center whatever I wanted broached on the lathe, and run the broach through it using the tailstock. You were pretty much guaranteed that the broach would be centered and perpendicular to the hole, and the tailstock we had could generally handle the forces involved. I realize that it wasn't the greatest for the lathe (especially the ballscrew on the tailstock), but we rarely broached anything thicker/more intense than 1/2" aluminium, and didn't seem to have any issues with the lathe.

[Cory]

Originally Posted by DampRobot

On 100 I used to center whatever I wanted broached on the lathe, and run the broach through it using the tailstock. You were pretty much guaranteed that the broach would be centered and perpendicular to the hole, and the tailstock we had could generally handle the forces involved. I realize that it wasn't the greatest for the lathe (especially the ballscrew on the tailstock), but we rarely broached anything thicker/more intense than 1/2" aluminium, and didn't seem to have any issues with the lathe.

the biggest problem is with the spindle bearings, not the nut in the tailstock. The spindle bearings are not designed to support an axial load when not rotating.

[matthewdenny]

Would something like this work?

http://www.harborfreight.com/20-ton-...ess-37999.html

[aldaeron]

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?

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-

[Cory]

Originally Posted by matthewdenny

Would something like this work?

http://www.harborfreight.com/20-ton-...ess-37999.html

Sure, if you don't mind all the downsides that have been pointed out about this style of press. If you're going to be broaching a lot, get a 4 or 5 ton lever operated arbor press that will allow you to broach in one shot. You'll spend twice as much but it will be 5-10 times faster and easier to setup.

[aldaeron]

Originally Posted by Cory

Sure, if you don't mind all the downsides that have been pointed out about this style of press. If you're going to be broaching a lot, get a 4 or 5 ton lever operated arbor press that will allow you to broach in one shot. You'll spend twice as much but it will be 5-10 times faster and easier to setup.

Recommendation? Pretty please?

Not sure we would buy one yet, we're on the cusp of "it's annoying but a better tool is expensive and this one works"

[Cory]

Originally Posted by aldaeron

Recommendation? Pretty please?

Not sure we would buy one yet, we're on the cusp of "it's annoying but a better tool is expensive and this one works"

We've had this for 6 or so years now and it works great.

[AustinSchuh]

Originally Posted by Cory

We've had this for 6 or so years now and it works great.

Almost works great. I've spent countless hours with your arbor press, and the head isn't perpendicular to the table. The end result is that if you don't re-square the broach up in the middle a couple times, it'll broach crooked. I end up with like 70% yield and 5-10 minutes per part.