Presses and techniques for 1/2" HEX broaches

[asid61]

Originally Posted by thinker&planner

I actually brought home a 3.5" dia 14" stroke pneumatic piston form my summer job, with the intention of converting our press for broaching, but nobody took me seriously, so nothing got done. And now nothing will before build season.. :/

And we actually made a little piece to go on the end of the hydraulic ram, but it is not long enough to hold the broach straight, just in the center of the ram.

I calculated that that cylinder only puts out about 1000lbs of force on 100psi. Were you planning on adding a lever arm or something, or is that enough to force a broach though?

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?

[Greg Needel]

Originally Posted by asid61

I calculated that that cylinder only puts out about 1000lbs of force on 100psi. Were you planning on adding a lever arm or something, or is that enough to force a broach though?

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?

Keeping broaches straight is something that is hard for students (and some mentors) to do without a fixture or jig. Over many year I have seen students kill tons of sprockets, gears & hubs due to a crooked broach). The thickness of the part you are broaching and the material plays a big part in this (the thicker the better).

[thinker&planner]

Originally Posted by asid61

I calculated that that cylinder only puts out about 1000lbs of force on 100psi. Were you planning on adding a lever arm or something, or is that enough to force a broach though?

I honestly have no idea. I wish I knew, because then I might pursue it further.

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?

We broached some HTD 5mm pulleys that were 1/2" wide, and a few of them came out crooked. This was probably due in part to poor technique (and execution), but I would not trust most of our team members using our current setup for high-speed applications. (where the broached piece is running at high speeds)

[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

[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.

[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.