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Author Topic: Mold Clamping  (Read 674 times)

Bob La Londe

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Mold Clamping
« on: August 21, 2016, 01:00:17 PM »
On one of the tackle making groups I read somebody mentioned clamping, using boards as load spreaders, and not liking C-clamps.  There are using a pressurized injection system made by another mold maker.  Before I post my reply I'd like to mention that I make all my molds with clamping screws for safety.  Some people choose not to use the clamping screws in favor of other faster methods of clamping and un-clamping. 

"I only hand inject my own baits, but I use the heck out of Harbor Freight bar clamps.  I feel like the average HF quality has gone down hill since the kid took over the company, but its pretty hard to screw up a bar clamp.  (Irwin actually managed to screw some up so they wouldn't hold though.  LOL)  I have a bunch of these http://www.harborfreight.com/6-in-quick-release-bar-clamp-62239.html hanging over my pouring bench.  Well actually at the moment they are packed up in boxes with the rest of my pouring supplies while I do some work in the shop. 

A few times I've done work where I needed a shorter clamp.  The bar just got in the way.  At $2.99 each throwing it in the band saw to shorten it bother's me not in the least.  I realize in your case the tightening handle may get in the way.  Cut it off, find the thread, and double nut the screw.  You can still quickly spin them down, and once you get the rhythm having a wrench the right size at hand on the bench to snug off will go just as quick as a slide bar on a C clamp.
 
They come with plastic pads, but I take them off and toss them in a drawer in case I ever want to use them for something I do care about the finish on, but for my own personal molds I could care less what the outside looks like as long as the inside works right.   To be honest though they really don't do any damage you couldn't buff out by hand anyway.

As to uniform pressure... if you really want to go there... a trick used in some types of wood working is a slightly arched board.  I hesitate to say uniform clamping, but it does spread the clamping force over a larger area.  If using two end clamps the board is arched away from the stock at the ends.  If using a single center clamp the board is arched away from the stock in the middle.  When I used to use my parrot vise for molds I use aluminum plates machined to do the same thing.  A slight arch, and close a hair past touching all the way across.

And the last of the immediate thoughts I had when I read your post.  You mentioned having to run 20PSI on your pot(s).  I assume that is high.  Since I only hand inject I don't know.  I do however have some personal molds that are 20 cavities or more.  One little finesse worm I shoot has 30 cavities with fairly thin curly tails.  They all fill to the tips with modest steady hand pressure if I run the plastic just a little bit warmer.  I usually use 4 clamps on that mold when I first shoot it, but when I am making my personal summer stock of them, I get in the rhythm, and the mold gets warm I only need two.  Maybe a few degrees bump in temperature can help lower your required pressure to fill it.  Again I only hand inject for my own use so I can only say it might be worth a try, but I don't KNOW it will work for you."


In a reply somebody said they would just weld a handle on the shortened screw in the bar clamp.

That is a great suggestion. I tried to think of things that anybody could do with basic hand tools. For my own use if I needed to do that I'd probably turn and thread the screw to fit a standard knob/handle so I wouldn't need a wrench, and then use a back stop nut to clamp it in place so it wouldn't back off when loosening the clamp. That's if I couldn't find a modest priced knob that fit the stock thread. Or I might thread an unthreaded knob to fit the stock thread.

Between McMaster, Reid Supply (or whatever they are called now), Carr Lane, and maybe Zoro Tools you should be able to find a knob to fit just about any thread.

Not everybody has a lathe or even a welder though.

Since I hand inject it doesn't get in my way anyway.



Bob La Londe

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Re: Mold Clamping
« Reply #1 on: November 19, 2017, 08:49:56 PM »
These are only 2.99 each.  I can't see why anybody wouldn't use them.