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Posted: 12/2/2007 6:04:08 PM EDT
I am going to start making my own custom Micarta knife scales (handles). I need to press the stack with roughly 500-600 lbs of pressure between two plates. I'm thinking of getting two 10" x 10" steel plates and either buying a press from Harbor Freight or making some Rube Goldberg jig with big C-clamps.

Does anyone know how to determine how thick a steel plate I need that it will not deform any measureable degree under 500-600 lbs pressure applied either in the corners (C-clamp method) or solely in the center (a press)?

Thanks!


CWO
Link Posted: 12/3/2007 3:43:11 AM EDT
get a cheap ball bearing press from harbor freight

I'm a big fan of overkill so I vote 5/8"
Link Posted: 12/3/2007 4:15:07 AM EDT
Pounds is a measure of force, not pressure. Pressure is in pounds per square inch. Do you mean a force of 500 lb.s applied to the plate or 500 psi applied across the plate?

How do you plan to apply the pressure to the material (micarta)?

What you are describing is a simple molding press. If you are applying 500 psi to the molding material, the force in pounds to keep the press from opening will be 500 psi times the projected area of the molded object viewing it from behind the mold plate. In other words, if the molded part has 10 sq. inches of projected surface area held at 500 psi, the force to hold the mold closed would have to be just greater (say 10% more) than 5000 lb, or 2-1/2 tons. This is not a lot by molding standards. My smallest molding press (for comparison) is 100 tons. Our molding pressures are typically about 3,000 psi.

Rather than making the mold plates from solid heavy plate, you can also weld or bolt stiffener sections to the back of a thinner plate. This would likely be less expensive than a solid plate.

If I knew more about what you were doing I am sure I could help you.
Link Posted: 12/3/2007 5:19:19 AM EDT

Originally Posted By beemerphile:
Pounds is a measure of force, not pressure. Pressure is in pounds per square inch. Do you mean a force of 500 lb.s applied to the plate or 500 psi applied across the plate?

How do you plan to apply the pressure to the material (micarta)?

What you are describing is a simple molding press. If you are applying 500 psi to the molding material, the force in pounds to keep the press from opening will be 500 psi times the projected area of the molded object viewing it from behind the mold plate. In other words, if the molded part has 10 sq. inches of projected surface area held at 500 psi, the force to hold the mold closed would have to be just greater (say 10% more) than 5000 lb, or 2-1/2 tons. This is not a lot by molding standards. My smallest molding press (for comparison) is 100 tons. Our molding pressures are typically about 3,000 psi.

Rather than making the mold plates from solid heavy plate, you can also weld or bolt stiffener sections to the back of a thinner plate. This would likely be less expensive than a solid plate.

If I knew more about what you were doing I am sure I could help you.


BP: Thanks for your insight. My current approach is to create a sandwich of cloth and epoxy approx 3" x 6" (but possibly as large as 9" x 6") and to place it between two steel plates and apply ~500 lbs of force to the upper plate - driving excess epoxy out of the sandwich and using even compression to hold the sandwich under that pressure for approx. 24 hours until dry.

A press from HF is going to use a jack - which appears to exert force at a single point. I want to make sure the top steel place does not deform noticeably under pressure - so the sandwich maintains equal dimension from end to end and side to side.

I could use large C-clamps - but adjusting them equally and individually has the same problem - possibly x 4.

I'm trying to visualize and implement a means to apply pressure evenly (from the sandwich perspective) that is simple as possible and doesn't call for a lot of fabrication (I can't weld) and isn't a huge PIA every time I make micarta.

Thanks for any insight you can lend!

CWO
Link Posted: 12/3/2007 4:09:26 PM EDT
This is a press set-up that I have seen:




It looks like he uses 4 steel blocks of increasing footprint - the 4th being the main top (and largest) plate - under which you can see the cloth sticking out.

While I understand the concept of how he is distributing pressure - a stack of 4 seems a little unusual.
Link Posted: 12/3/2007 4:36:02 PM EDT

Originally Posted By CWO:While I understand the concept of how he is distributing pressure - a stack of 4 seems a little unusual.


It is probably just what materials he had around to stiffen it and it looks like it would work fine. The force you are using will not be difficult to distribute. Suggestion: Use a 1/4" (or thicker) plate for the top plate and weld or place two lengths of 2x2x1/4 (or larger) angle iron with the 90 degree angle up (the two ends of the angle touching the plate) so that the four lines of contact of the angles to the plates are equally spaced along the longer dimension of the plate. On top of that at 90 degrees from the direction of these angles and along the centerline of the long dimension of the plate, place another stiffener. It can be another piece of heavy angle iron, a short piece of I-beam, or a piece of rectangular tubing. Look again for a minimum of 2" section widths and 1/4" flange thickness. More is always better.

Your press will push down on the center of the last stiffener. It will transmit force to the stiffeners on the plate which will spread the load on the plate. This is only one of a thousand solutions to the problem. If you want to get scientific, you can buy pressure indicating film to see how uniformly the pressure is being transmitted. This is probably overkill for your application..

pressure indicating film
Link Posted: 12/3/2007 5:11:32 PM EDT
BP: I appreciate your advice on this. I'm going to give it a shot.

Regards,

CWO

Link Posted: 12/5/2007 8:01:04 AM EDT


A two inch by six inch 5/8" thick general steel plate (20,000 PSI) will deflect .004 of an inch at 500 pounds per square inch with the pressure being applied in the middle only.

If you use a 3/4 inch plate you will be fine. If you weld some gussets you will be in even better shape.

I will try and post the calculations.

Good luck,
Link Posted: 12/5/2007 5:41:42 PM EDT

Originally Posted By AR9mm:

A two inch by six inch 5/8" thick general steel plate (20,000 PSI) will deflect .004 of an inch at 500 pounds per square inch with the pressure being applied in the middle only.

If you use a 3/4 inch plate you will be fine. If you weld some gussets you will be in even better shape.

I will try and post the calculations.

Good luck,


Thanks - very helpful of you. I hadn't thought of the gussets.


CWO
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