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Is my vacuum chuck gauge broken?

Joe Cornell

Joe Cornell

Joined
Jan 3, 2006
Messages
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Location
Kenmore, WA
It has not been used in several years and I see now it reads negative 19 mm Hg with no pump attached. This is the MAKI gauge sold by Craft Supplies. I don't see any instructions about how to adjust or calibrate the gauge in the printed materials that came with it.
 
is it important

It has not been used in several years and I see now it reads negative 19 mm Hg with no pump attached. This is the MAKI gauge sold by Craft Supplies. I don't see any instructions about how to adjust or calibrate the gauge in the printed materials that came with it
Click to expand...

You may be able to remove the glass at the front and adjust the pointer.Also you could just minus the 19 off the result as you use it.
But is the number that important? As long as you have vacuum and the chuck holds well the number is not so important.
 
I think that most pressure and vacuum gauge consists of a partial turn coil of semi-flattened tubing (aka Bourdon tube) with a clock type spur gear connection to the pointer. If something has gotten out of whack (possibly caused by a hard whack), then the gear works may be binding. If you are the brave sort who does not mind possibly finishing it off for good, you could open it up and see if you can relieve any binding. I usually figure that there is not much to lose in a situation like this and curiosity is one thing that I have in ample supply.
 
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Pin hole at top

Thanks for the suggestion.

There is not really a pin hole but I was informed by Roger at Craft Supply, USA that there is a lever at the top of the guage to equalize the pressure. I will give it a try and post the results here.
 
Bob Chapman said:
Does it have a small rubber seal at the top? If so, there should be a pin hole through it to allow pressures to equalise (I think) when it's not under vacuum. Sometimes the hole gets blocked and the needle doesn't quite return to zero. Take the rubber out and clean it and see if it makes any difference.

Bob
Click to expand...

This type of gauge measures differential pressure of the source compared to ambient atmospheric pressure. The case is not sealed at all (except in the case of glycerine filled types -- the glycerine is for pointer dampening) -- it is just a housing to hold the mechanism which consists of the Bourdon tube and gear and lever arrangement that connects to the pointer. The instrument would work just as well if the bezel and dial scale were removed -- you just would not be able to read its measurement. Even in the liquid filled units, the inside of the housing is virtually at ambient atmospheric pressure.

joecornell said:
Thanks for the suggestion.

There is not really a pin hole but I was informed by Roger at Craft Supply, USA that there is a lever at the top of the guage to equalize the pressure. I will give it a try and post the results here.
Click to expand...

Most of the low cost vacuum gauges don't have provisions for zeroing out offset error so if yours has an adjustment screw that is fortunate.
 
Well, there are two screws on the back of the gauge. I don't see how they could be connected to the dial but what could it hurt to try turning them...

The unit is liquid filled. I just assumed it was oil but it could be glycerin.

Thanks for the advice.
 
joecornell said:
Well, there are two screws on the back of the gauge. I don't see how they could be connected to the dial but what could it hurt to try turning them...

The unit is liquid filled. I just assumed it was oil but it could be glycerin.

Thanks for the advice.
Click to expand...

Uh uh, don't touch those unless you want to disassemble the gauge to put everything back together. Those two screws hold the outer housing shell to the brass manifold that holds everything else together. Also, those two screws are very short and it is easy to drop them.

On the other hand -- go for it. Experience is best way to gain knowledge even if the experience is learning why you shouldn't have done it. I'll dispense with saying how I came about that bit of wisdom. 😀
 
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Thank you for the advice Barry!

Well, I turned the lever at the top and to my surprise a sticky clear liquid came out. I left it open util the gauge went down to zero. I assume this means the liquid was glycerin.

Roger (from Craft Supply) was right and, as it turns out, I did not need to "learn" anything by turning the screws.

All's well that ends well.

Now I just need to save up enough for a vacuum pump...
 
You're welcome, Jim. Glad to see that there was no need to buy a new gauge. Liquid filled gauges are a bit more expensive than the garden variety gauges so at least we know that Craft Supplies provides a good quality vacuum gauge.
 
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