Hydraulic Punch hole size question

HRS (hot rolled steel) is often supplied with a

10% over to 5% under tolerance by weight. As a rule of thumb for punching holes use a die clearance for the bottom die of 10% of the material thickness. In that case the resulting hole will be very close to the punch size for the top 1/3 of the material thickness. From there the bottom 2/3 part of the hole is torn out and tapers to the die size. If you want to punch holes for 1/2 square HRS bars a 9/16 square or larger punch should work. HTH.

HRS (hot rolled steel) is often supplied with a

10% over to 5% under tolerance by weight. As a rule of thumb for punching holes use a die clearance for the bottom die of 10% of the material thickness. In that case the resulting hole will be very close to the punch size for the top 1/3 of the material thickness. From there the bottom 2/3 part of the hole is torn out and tapers to the die size. If you want to punch holes for 1/2 square HRS bars a 9/16 square or larger punch should work. HTH.

Better going 9/16".The punch will punch the proper size.One of the problems with punching the holes in the rails is that you will have to straighten it after and it can be a bit time consuming.You will need

14 tons of pressure for that size. Regards,Mark.

I would use a 17/32 punch as long as you can punch the holes square as possible to the bar. 9/16 would give you a little more play with the vertical pieces enabling you to make sure they are square to each other.

The rule of thumb is that when blanking out parts, the die controls the size with the clearance on the punch.. When punching a hole, the punch controls the size with the clearance on the die.

Personally, I feel clearances called out by some sources are a little tight. Of course, I'm not knocking out just a few holes on a slower hydraulic machine. For 1/4" HRFB I would run up to .050" clearance. That ensures me the cleanest holes and longest tool life on thousands of holes done in the punch press. You have to know on clearance callouts if they are talking a certain percent per side or total clearance.

Good luck. Les

My question would be why bother to pinch any holes? Just make a jig to position your vertical posts and weld away.

For the legs, just weld on in line with the upper posts.

Thanks for the responses!

Roger: I think it would be faster to punh the holes than welding/jig building. plus I now have a reason for building the press :-)