PDA

View Full Version : Hole punching



red
04-13-2003, 12:36 PM
I finally obtained a hydraulic press better than I ever hoped to obtain in Jan. this year. I want to try building a punch unit with approx 6 inch throat. I need advice on material to make ram out of. The rod will be threaded to except punch coupling nut from piranha iron worker and use iron worker punches and dies. I am thinking that a design similar to unipunch but with adjustable die retainer. I have no idea how much spring return I need to pull punch out of hole. I first thought of making adapter to go into press ram to hold punches. but the head of press can be moved left and right and the press bed has play as well. I need to be able to punch a 1/2 hole in 1/2 inch plate. Any advice would be appreciated.

L Webb
04-13-2003, 03:01 PM
Not knowing what your hydraulic press looks like or tonnage capability makes it tough to answer your question.
A 1/2 hole in 1/2 mild steel will require 20 tons. Shear angle on the punch can reduce that.
I don't have my charts in front of me but stripping forces will be quite high for that.
Ironworkers have the easiest method to strip. As the punch cycles upward, the material is forced off the punch by the fixed plate.
I use several methods to strip on my punch presses including fixed stripper plates. It all depends on the die set and application.
Pictures and more info can result in a better answer to your questions.
Les

SJorgensen
04-13-2003, 05:08 PM
It seems to me that a spring would be hard to rely on for extracting the punch. But a double acting hydralic ram is guaranteed to extract. Be sure and share with us your final design and results.
Thanks,
Spence

red
04-13-2003, 06:11 PM
Glad to see a response so soon! The press is a 50 ton Dake elecdraulic H frame. the bed has a winch and can be lowered to floor. The press has a spring return feaure for the ram. From the blowup of the parts it looks one spring inside the other. I want to make a stand alone c-frame attachment. The punches apparently are all the same lenght. The dies are the same diameter and depth. I plan on using solidly mounted srippers similar to iron worker. I dont want it to be more than 12 inches high. the ram will slide in a block that has screws similar to gib adjust screws to keep ram fit in block close coupling nut will thread into or onto ram to retain punches. I have studied various machines and they all use about the same setup. I have been thinking about getting a piece of 4140 prehardened but Have never tried to thread it. I use carbide threading tools for most applications but dont know if there is a better metal to use for punch ram. I would like to someday make own punches and dies but the commercial ones are very reasonable at approx 18.00 a set.Plus special shapes like square hex etc. are readily available to. Many iron workers use stand alone notchers shears etc. But not hole punches. Unipunch and strippit units are good but it seems to me
that it is hard to see where punch is hitting metal. These units are generaly used on fixtures. anyway I wont be out much trying.

L Webb
04-14-2003, 06:24 PM
I have seen many people think a 20 ton H-frame press is good for 20 tons of punching pressure from a bottle jack. It just isn't going to happen.
Your 50T may develop good tonnage but whether it is stout enough is the question.
Punch presses and ironworkers have pretty beefy frames and for good reason. Rigidity is a must when doing heavy punching.
All my punch presses are also backgeared. Flywheel presses just don't have the oomph for heavy punching.

The formula for stripping force is as follows: P = L X T X 855
P = Force, in pounds, to strip
L = Length of cut. For round holes it is the circumference of punch faces.
T = Thickness of stock being cut.
1/2" hole in 1/2" MS will require about 672 lbs of stripping force.

Good luck.
Les

trap
04-15-2003, 12:46 AM
I play with flywheel punches but have never seen a backgeared punch ..... could you take that big stick and beat some more "smarts" into me ...... please !!!!

red
04-15-2003, 10:30 AM
Thanks for all your replys! The press should be stout enough I think. The springs in press cylinder may not have oomph to pull punch out of steel. I am looking to make a spring loaded fixture similar to unipunch but with more clearence to see punch better. 650 pounds pressure is a bunch. I might have to resort to four springs, two on each side of ram. I let you know how it works out. Not going to cut it if I have to clobber work to get it off the punch. Anyhoo it will keep me brainstorming for a while.

DR
04-15-2003, 11:11 AM
Red,

Instead of springs you might have better luck with a urethane stripper. This could fit over the shank of the ram. Check with Roper Whitney for various sizes or go direct to a urethane manufacturer like www.acrotechinc.com. (http://www.acrotechinc.com.) Personally, I would size the stripper for far more than the 672 pounds Les calculated. That's only an approximation and it can go higher.

As to the material for your ram, mild steel probably would work. But if those punches mount similiarly to the Roper Whitney style you'll need a hardened insert to absorb the force at the end of the punch.

L Webb
04-15-2003, 11:25 AM
I'll see if I can take some pictures of the backgearing and post them. It's kind of hard to tell from most pictures of presses whether they are backgeared or just flywheel unless you know what to look for.
Flywheel OBI presses are a dime a dozen. When the description in an ad includes "BG", the price goes up fast for a decent machine.
The big difference is the flywheel drives gearing to move the crank instead of just driving the crank. Slower, but more power.
Les

Thrud
04-15-2003, 12:21 PM
Red

Considering how cheap a unitool punch & frame is on eBay I would just find a frame large enough for your needs and then you can manufacture punch & dies for your needs. Some of the larger units can use shaped punches. The use readily available springs and parts - this is the easiest way to go.

It is difficult to make what you want accurately and strong enough - if the punch & die are not accurately positioned in relation to each other you are only going to shatter the tools. S-7 is a good choice for home brew punches & dies as it will take lots of impact.

red
04-15-2003, 11:40 PM
Thanks for you input thrud, My first thought when I saw the unipunch website was this is exactly what I want. Unfortunately I passed on a large one on e-bay that had a 1/2 inch capacity. I havent seen one since. But Im sure this size will pop up again.I still think a homade frame unit should work Iron workers use manual punch aligners witch are fancy words for "it goes thru the hole so it is aligned" Ridgity wise, the forces are going to be pretty much Straight down. Even better than an iron worker because they use a lever to push ram down witch induces side thrust You guys may all be right but Im stubborn and willing to try. I sometimes wonder if I buy machines just to see if I can come up with different ways of using them. Most of the time everything I want has been done before and there are machines available for the task. But fabricating kind of gets in your blood.
And the relentless quest for something new takes over.

Thrud
04-15-2003, 11:51 PM
Red
1/2" is not big - I have seen Uni-tool 4" punches! When they get broken from not setting the press correctly - they make great boat anchors. Had Uni-tool notchers take that same trip...

Yep, $2,000 blue boat anchors.