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Dead weight gauge Tester - weights


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  #1  
Old 05-24-2008, 05:50:03 AM
Peter Peter is offline
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Default Dead weight gauge Tester - weights

Today, I purchased an Ashcroft dead weight gauge tester Model 1312.

It looks the same as the pictures shown in the 1300 instruction plate posted here. I am missing the weights and like to ask if anyone with an ashcroft could weight 100 pounds worth of weights and post the results. Or better yet, are the specs available for those weights?

I was thinking I might make a set of weights using lead shot in some old electrical tape metal tins. I am open to other ideas, including how to get an accurate weight of my home made weights.
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Old 05-24-2008, 08:38:53 AM
K D Redd K D Redd is offline
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Default Re: Dead weight gauge Tester - weights

I made some wieghts for a Rockwell Hardness Tester I save from a scrap yard. I needed a total of 15 pound broken up into a 6, 5, and 4 pound wieghts. I used some 3 inch shafting I had. I started with my Machinist handbook which gave me the density of the steel in wieght per cubic inch. I calculated the lenght of shafting I need to make the weights. On the 5 and 4 pound wieghts I had to drill a hole in the center and cut a slot through the side with a bandsaw so I hang them on the 6 pound wieght so this removed material need to be takewn into account when I made the first cuts of these two weights. One I did not cut long enough so I had to weld so small pieces on each side. After I made these wieghts I took them to the local grocery store to wieght them. This was many trips because they were heavy so I would go to the shop and drill out material from the face of the wieghts. I finially go them where the 6 LB wieght weighs 6 pounds, the 5 LB wieght weighs 5 pounds, and the 4 LB wieght wieghs 4 pounds. You put them all on the scale and the total wieght was 15.01 pounds. I know this is not tracable to the National Bureau of Standards like some of the parts I got for the tester were, BUT got the unit adjusted so I am within a 1/2 point of my test block of the TOP of the Rockwell "C" scale and about one point off the test block that covers the bottom of the "C" scale and the TOP of the "B" scale. To me this is close enough for GOVERMENT WORK.

Kent
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Old 05-24-2008, 08:59:36 AM
Nick Stanley
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Default Re: Dead weight gauge Tester - weights

I don't have a set of Ashcroft weights to weigh, but, you could ask Ashcroft: http://www.ashcroft.com/contactus.cfm

Or:

Measure the diameter of the piston on the tester, and find the area of the piston/cylinder based on this.
Since Pressure=Force/Area,
you can take that area multiply it by the change in pressure you want on the gauge, and you will end up with the force, or the weight that you will need on the piston to get that change in pressure. The piston will almost always be an even fraction of 1 sq. in. area. Mine is 1/8 sq. in. This means that a 1 lbf. weight added on top of the piston will produce 8 psi on the gauge.

Now, you still need to know the pressure due to the piston and weight platform alone. You could find this by connecting a good gauge and noting the reading, as was mentioned. It is probably standard; mine is 5 psig. A more accurate way would be to either have the piston and weight platen weighed on a good balance.

I'm not familiar with your Ashcroft tester, but is it the type with a hydraulic hand pump connected to the piston and weights? If so, there may be one pitfall. One of these testers that I have used, a high pressure tester, had one weight in the set, marked, say 1000 psig. This weight had a groove cut around the perimeter to identify that it weighed less than the others. This weight compensated for the weight of the piston assembly. Eneve thought the weight alone was lighter than that necessary to produce 1000 psig, when combined witht he weight of the piston, the reading would be 1000 psig.

Another thing to remember in making your own weights, is that any error in the actual mass of the weight will be magnified by having a piston of less than 1 sq. inch. For example, with a piston of 1/8 sq. in. area, an error in a weight of 0.1 lbf., will produce an error at the gauge of 8 times that, or 0.8 psig.
Make sure you give the weights a slow spin when testing to get a true reading.
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Old 05-25-2008, 10:58:13 AM
Peter Peter is offline
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Default Re: Dead weight gauge Tester - weights

I measured the diameter on the shaft. it moves freely but seemed to bind up when I tried to pull it off, so...I measured in place I get 0.440. Thats very close to 7/16 (0.4375). Either way --Thats an odd size, why not just use 0.500.

Nick, following your advise - squaring 0.440, would set 1 psi with 0.1936 pounds. And 19.36 pounds would be 100 psi. What ugly numbers! Did Ashcroft do this deliberate?

The platen is stamped 25. I'll guess that 2.5 psi worth.

I don't have a good scale, and I dont think I am up to an Archimedies method. I guess I will wait for a while,.... it not like this tester will be lonely sitting along side other unfinished projects........
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Old 05-25-2008, 08:08:58 PM
Pete Deets Pete Deets is offline
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Default Re: Dead weight gauge Tester - weights

Hi Peter,
Good detail information is also at http://www.ashcroft.com/library/1305D.pdf

I would guess (and guess only) the 25 stamped on your weight table indicates a reading of 25 psig. I'd suggest putting on a low range gauge to verify. If that is the case, then your 1312 may well follow the same pattern as a high pressure 1305. The actual weights work out to be:
.3125 lbs actual for 25 psig
.625 lbs actual for 50 psig
1.25 lbs actual for 100 psig
2.5 lbs actual for 200 psig

As for weighing your own weights, are you on speaking terms with the folks at your Post Office? A quick reading from a postage scale may be of help and had better be accurate.

Please let us know how you progress......PD
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Old 05-27-2008, 09:21:33 AM
Peter Peter is offline
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Default Re: Dead weight gauge Tester - weights

Thanks pete,

I studied the 1305 web page (to day) and I see they have a low pressure weight option with a ratio of 1:16. Great! That would mean 1 oz = 1 psi. How convient. I calculate that shaft diameter would be a 1/4 inch diameter for the new ashcroft 1305 in the low pressure range.

I still just dont get a 0.440 diameter on my old 1312?

Last edited by Peter; 05-27-2008 at 04:33:58 PM. Reason: Please forgive this math error
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Old 05-27-2008, 01:25:54 PM
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Default Re: Dead weight gauge Tester - weights

A 0.440" shaft has a square area of 0.15205 Sq. In.
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Old 05-27-2008, 04:33:16 PM
Peter Peter is offline
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Default Re: Dead weight gauge Tester - weights

Oops. I got that wrong that all the way down. I was thinking 1" diameter was 1 sq inch. And I could take a ratio of the diameters. Dumb.

Ok.

pi * 0.220 ^2 = 0.15205...

and that would mean every 0.152053 pounds of weight would be 1 psi on the gauge. I hope.

Now I wonder if this is some convient even number of grams or fraction of an ounce?

Maybe I need to try a micrometer for a good diameter reading.
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Old 05-27-2008, 06:08:17 PM
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Default Re: Dead weight gauge Tester - weights

That's right about 69 grams. I think a micrometer might be a good idea, since the really small sizes you're dealing with need a lot of precision measurement to calculate properly.
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Old 05-28-2008, 11:21:53 PM
Pete Deets Pete Deets is offline
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Default Re: Dead weight gauge Tester - weights

Peter,
Please forgive the broken record but have you had a chance to try just the weight table and a low range gauge?....PD
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Old 05-30-2008, 07:09:38 PM
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Default Re: Dead weight gauge Tester - weights

Pete, Your suspicion are correct! the 25 on the table corresponds too 25 psi without any weights. Obviously this was not intended for those 15psi heating boilers. It is marked US Navy with a brass tag the cover.

I see there is a certain finesse' to using the tester. The table will stick and readings will vary quite a bit unless I ever so gently spin it around and twist the pump back a forth a bit to keep the weight height in the sweet spot. Its fun to use,... not your push a button and read a number deal.

Here is a picture of the tester in action.
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Old 05-30-2008, 08:47:52 PM
Pete Deets Pete Deets is offline
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Default Re: Dead weight gauge Tester - weights

A nice looking find, good for you! I haven't worked with that model, but I'm guessing perhaps the weight table is captured in place by that brass collar just under the table. On the 1300 if you crank in the handle too much you WILL send the weight table, weights & enough oil to make a real mess into orbit. I don't think you'll have to ask how I know. That brass collar may well be threaded into the top of the cylinder to prevent this from happening and if it unscrews you may be able to remove the piston completely. If you can get it out & weigh it, you'll have your ratio.

Yes, I would expect the machine to be a bit fussy as you try to make it work at it's absolute lowest range. All I've handled have done the same and adding weight to check a higher pressure seems to calm them down quite nicely.

I have a 1300 that seems sticky, too and plan to try flushing it out with some very light oil and see what happens. You may want to consider doing the same with yours or it may free up with use. Hard to say what kind of deposits may have been left on the innards by the oil and possibly a bit of condensation here & there.

I find it fun to test gauges for folks as it always draws onlookers & questions and does require a bit of finesse. Were the pictures of the instruction card in the other thread detailed enough for you? If you want, I'm pretty sure I still have the original jpegs & could e-mail them to you. PM me on that if you want them.
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Old 05-31-2008, 01:05:08 PM
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Default Re: Dead weight gauge Tester - weights

Removing the big knurled nut revealed a keeper/threaded collar, again, just as Pete had predicted. I have the metal instructions inside the lid of the box. All set there. We need a double - thank you button.

A surprise to me - the piston diameter is stepped down to a small 0.1765 - 0.177 inch diameter. About this I don't care anymore. using the table was the key to happiness.

I have made up a set of 3 weights that will allow me to check: 25, 50, 75, 100, 125, 150, 175, and 200 lb settings. Using three weights 25,50,100 plus the table for another 25. I started with the table and made an exact duplicate using an tin container and lead shot. With that I used the combined weight of 25+25 to make up a 50 and then combined those to make a 100. This old scale is very sensitive. I was pulling out 7 1/2 and adding 8's and 9's to dial the weight right on. I think I am pretty darn close.

I am starting to wonder if the original weight sets were calibrated to match a specific instrument or are they interchangeable?

As for the cleaning it made a big difference the large 0.440 diameter was coated with a varnish like layer on the inside (far) end. Now with that cleaned and oiled it moves slick as can be.
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Last edited by Peter; 05-31-2008 at 01:23:48 PM.
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Old 05-31-2008, 04:50:14 PM
Pete Deets Pete Deets is offline
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Thumbs up Re: Dead weight gauge Tester - weights

Good For You all around! It is great to see & read the positive results. You've proven again that a picture is worth a thousand words. Had you not posted the first picture I would have never known about the collar & guessed at its purpose.
Math was never my strongest suit but it looks like you've got a 1/40th square inch piston shaft so the actual weights listed earlier should give you half the listed pressure indication (I'm happy to have anyone double check my assumption & let me know if it is wrong). That's also a quite nice looking balance scale you have and I would bet about the best tool for the job.

As far as interchangability of the weights & testers, I certainly hope that it is so. I've bought a couple of testers here & weight sets there but have not yet taken the time to put them all together.

Have fun with your new machine!......PD
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