doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Question on Wall Thickness Gage

Thanks Gnoman I will try McMaster-Carr, or there is one in Reading, can't think of the name.

As for the dial indicator on the tube, I pick it up and move the block along the tube in increments of usually 3" for readings, and let the stem down on the barrels.

I tried what you said by taking the barrels off the pillars and re-installing them. The reading was within .001 of the previous reading.

In the enclosed picture you can see the overhang of the alumium block with the indicator. The spring loaded needle takes up any movement and does not make the block rise because the weight of block and indicator over ride the spring tension.
That is my theory.

Bad picture of barrels mounted on gage.

JDW, I was one of those who appreciated the "Gaddy Spring" modification to the Manson gauge which insured barrel contact when using the gauge in a vertical position. Of all people, Jon Hosford showed me how to use the Manson gauge in a simpler and more accurate way, without a need for the spring or a way to hang the gauge vertically. Here it is, no fuss, no muss. Either put the barrels in a vise horizontally or have someone hold them hard to a table horizontally if you are at a show with no vise. Leave enough barrel free from the end of the table to use the full length of the gauge. Holding the gauge horizontally by the ball and suspending the other end by a rope, find zero. Yes, find zero. I'm sure everyone who owns a Manson gauge has a rope at the end opposite the gauge and ball. Hold the rope with one hand, insert the ball into the barrel and slide the ball down the barrel and observe the dial. Be sure the rod does not touch the sides of the barrel. Each barrel has three measuring surfaces, top, bottom, and side. With a cooperative assistant, you can measure all six sides at a gun show in just a few minutes if you have to. You will also have six measurements from the other end. Believe me, this method beats the hanging method by a mile. Thank Jon Hosford for this information.

David- .001 on removal/replacement (repeatability) is pretty good and you're not going to get better than that without exponentially difficult changes.

Nice pix- I now see how you've set it up. If it works OK you've lucked out but I really think you might wish to calibrate it or check its inherent accuracy with a tube of known wall thickness/uniformity.

I suspect the deformation of the lower bar is negated by the barrels - sort of a compensatory mechanism. Ordinarily a steel bar sags appreciably over that length.

Thanks Bill, I will look into that. My thoughts were different in what you said, I always thought doing the barrels horizontally with only one end firm, the weight of the barrels would deflect the bar no matter how careful you were, but reading your post clarifies that.

Off the top of you head, do you know what the diameter of the bar is, and how long is it?

Gnomon, I didn't see your last post as I was typing this one.
I looked in Grangers on-line, didn't see anything worth while, some of the brass and copper tubes had thicknesses with +/- .002. I found a piece of 3/4" copper tubing, I measured the thickness with a dial vernier caliper and it was also +/-.002 on both ends all the wall around. Before I cut a piece off, I laid a 24" straight edge along the length and it looked good. I cut a piece 31" long, cleaned the burrs on the O.D. and I.D. and placed it on the rod.
With the end butted up against the stop on the left, it read .040-.043, which I knew was too much. Read in increments of 4" turning tube to read all the way around, it was reading .032-.033 which is what I got on the vernier. Half way down it read .022-.017 and near the end on the right side read .032-.034. The inconsistant reading in the center tells me that the tubing could have a wow in it and it also was not near concentric. Thinking now, it doesn't sound like a wow, because I should have had a greater reading 180 degrees from the lowest reading. Don't know.

I think I definitly need to get another rod and have the balls drilled on a milling machine where I can have them perfectly inline with each other and also control the depth much easier.

I have nothing but time.

No, I don't know the exact diameter of the Manson bar, but it is small enough to be problem free in 20 gauge barrels but a bit big for 28 gauge. I don't know if reducing the diameter of the "ball" would make it suitable for 28 gauge. Maybe some reader would measure his Manson bar for us.

Doing some figures, for a 20 ga. rod, I'm thinking a 3/8" rod with a 1/4" bearing. With the bearing drilled in the rod half way, the total distance from top of ball to bottom would be 7/16" or .4375 which is alright for a 20 ga. bore of .550,

That would be nice to see.

More correctly, a "28" gauge bore would be .550. A 20 gauge bore is nominally .615.

Thanks for the correction Bill, too many numbers in my head.

To any concerned:

The diameter of both rods on my Manson gauge is .500".

The length of the rod that has the "ball" on the end - 18 1/2"overall. It is 16 1/2" from the "ball" to the block the rod goes into.

The length of the rod that hold the dial gauge is 16 1/4" from the center of the gauge stem to the block the rod goes into.
It is 18 1/4" from the center of the gauge stem overall.

I just got my Manson gauge yesterdayfrom Brownells. The Skeets bore gauge is backordered as they were out at the time. It should be here by early Feb. I should have bought these gauges 15 yrs ago when I started playing with these old doubles. I will never again say "I don't know BWT or bore size." For anyone who doesn't have a BWT or bore gauge, if you are going to keep buying old doubles,, it will pay to get one.

8bore - thank you for the clear explanation on how to use the Manson gauge horizontally. It is saved to my hardrive.

For anyone else interested, there was a hard "fiberglass" clamp that came with my Manson gauge. In the instructions, here is the explanation : "Alternatively, we now manufacture a reinforcing clamp-new design, pictured on page 1 - which may be pressed over the arms to assist with rigidity. Clamps are included with all new orders for Wall Thickness Gauges; If your WTG was ordered before we offered the clamps, please call us and we'll send you one for the price of postage."

thanks, redoftx

This is a very interesting thread on a clever design

Since Eightbore mentioned Jon Hosford, you probably know about his barrel thickness horizontal gauge, but if not look at:
http://vimeo.com/5011609
and
http://www.youtube.com/watch?v=sfBP7a0TbjM

Berrien