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Bedding compound shrinkage results

 
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  #1  
Old 11-27-2006, 08:23 AM
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Bedding compound shrinkage results

I conducted a little test to see if their were any real work differanced in the amount that differant bedding compounds shrink after curing. Here is what I did and the results.

I made some 1.500" square blocks out of Marine Tex ,
JB Weld , Brownells Steel Bed and Brownells Glasbed. All the blocks were allowed to cure for 12hrs then machined to a perfect 1.000" square and allowed to cure outside in the shade , the climate here has been ranging from 40deg F at night to 70deg F during the daytime with an average humididty of about 50% and allowed to cure for 5 days.
I collected all the pieces this AM and used my Starret digital mic. to make the measurements. and here are the results.

Marine Tex , had a shrinkage of less than .0001" from side to side and just barely .0001" shrinkage from top to bottom.
this stuff had a good consistancy was pretty easy to mix and work with and seeing that minimal shrinkage i can see why its popular with the custom gun crowd.

JB Weld , had a shrinkage or right at .0001" from side to side and the same from top to bottom.
I'm not sure that this is enough that it would cause any differance in accuracy. Seeing that this product is readly availabe at about any hardwear or autopart place it might be a good product for the average joe to try on a factory gun.

Steel Bed , had no detectable shrinkage in any direction !! I think that since I have to order Marine-Tex anyway that I'll be buying this stuff instead. Of all the compounds used this seemed to be the hardest to machine none of which were hard but this seemed a little less copperative

Glasbed , had no side to side shrinkage and just over .0002" shrinkage top to bottom.
I think that the top to bottom shrinkage and the lack of side to side shrinkage of this stuff was caused from some "sagging" maybe it wasen't totaly cured when it was machined and miced the first time.Overall , this product was the easiest to use as it was premeasured and easly mixed inna plastic pouch which the tip was cut out and the compound was easly squeezed out like icing a cake. This would probably be a great product for the average guy.

I'm not 100% convienced that one of these products are better than the other as far as accuracy goes but I can say that I'll be using the Steel-Bed from now on , its a little more expensive but I think that every little bit of extra insurance with worth the extra cost to supply the best job I can.
Another thing that may be of interist si that the action may expand and shrink as much as .0002 with a 30-50 deg change in temp so what effect would that have on the bedding or accuracy?
a test like this could go on and on for ever with the variables that one is likly to encounter with the differances in the thinkness of the bedding , the stock material and on and on. I just got to wondering why some products were used more often that others and some had never been heard of.
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  #2  
Old 11-27-2006, 12:37 PM
 
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Re: Bedding compound shrinkage results

Hi,

Very interesting results, Thanks.

Who makes "steel bed"?

Thanks, again.
C'ya, John.
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Old 11-27-2006, 05:33 PM
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Re: Bedding compound shrinkage results

Brownells carries it not sure who makes it for them.
the order number is 081-040-003 and the retail price is $40.50
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Old 12-05-2006, 04:02 PM
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Re: Bedding compound shrinkage results

Hey JD ,

Are you going to give the blocks a long term test---couple 3 months or more!?
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Old 12-05-2006, 07:34 PM
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Re: Bedding compound shrinkage results

I guess I could , I still have them they have been sitting here on my desk. I guess I can put them back outside to let them sit in the climate and see what happens.
Good idea , I'll put them back out on the deck tonight.
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Old 12-08-2006, 04:02 PM
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Re: Bedding compound shrinkage results

How much do your blocks weigh? Thanks.
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Old 12-08-2006, 06:24 PM
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Re: Bedding compound shrinkage results

I'm not sure , I don't have a small scale that will hold that much weight and my big ones only measure in 2oz incriments , the Steel bed is definatly heaviest probably 2oz the other are maybe 1-1.5oz , guessing
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