Measuring inside grooves

[chipmaker4130]

I'd start with a telescoping gage if the tips will fit in the groove. . .

How are you going to get the T-gauge out of the groove to measure it?

[jimsehr]

Here is a simple way to check groove location. Make a washer .200 wide 3/8 dia and ream it to fit your depth gage rod. Put washer on depth mic rod extended out from depth mic base holding it to rod with set screw. Now with depth mic rod extended about an inch longer then what you need to check groove location you use a gage block to set washer a set length from depth mic base. Now that you know washer face location you can use reading on depth mic to check groove width and location.

[BCRider]

Use an inside spring caliper to measure the diameter. Expand it so it just touches the widest point, compress and pull it out, let it expand again and measure it with a mike or dial/digital caliper.
For the width, you could buy a $15 digital caliper and cut off the outside jaws to fit it in the tube.

https://www.ebay.com/itm/15218000550...sAAOSwdzVXlTwM

My own outside spring style calipers are straight legged with just short "feet" at the ends. Perhaps it would be the right time to bend them for a little more depth into the grooves if needed. But the idea is certainly sound.

If the thimble on the screw isn't a little stiff be sure to pinch the thimble and screw as you spring the legs in to extract the calipers and don't release the grip until the legs are sprung back out. A slight movement is far too easy otherwise.

And since it's very much a touchy feely sort of thing you'll likely want to practice on a known size good smooth bore first. There was a thread a year or two ago about using spring calipers as an option to telescoping gauges. I got all enthused and tried it myself. It took a dozen or so tries to get the right feel and consistency. But once you get the right feel for the calipers being in contact you can nail the readings. It was likely 12 to 15 learning attempts before I was able to get readings that were all within a thou of the right size. About the same as it takes to learn to nail the right feel with telescoping gauges. Old world skillzzz.....

Reading down the first few posts I was thinking cheap pair of calipers and cutting the outside jaws as well. Looks like there's a number of us that think the same way....

Another option would be to make up a set of pinch calipers for doing the width of grooves on ID's just like you're doing here. At the most basic the two parts might look like this sketch. To use them just slide one past the other so the two straight parts of the tips touch the edges of the groove. Pinch to hold the setting, remove and measure. Extras to allow sliding and locking can be added to suit. And size could be adapted to fit into some pretty small bore sizes.

[gzig5]

I'd start with a telescoping gage if the tips will fit in the groove. If not, I would take a couple ball bearings and place them in the groove with stiff grease to hold them and then measure over the balls with a caliper or preferably a telescoping gage or inside mic. A pair of 3/16" balls can be had from most decent HW stores pretty cheap.

[Captain K]

This is the groove for the rod seal in the gland. The gland will be 1 1/2" thick and the groove will be centered in the thickness. 2-3/4" is not big enough to get calipers in. Although I just had a brain wave that I could cut the outside jaws off a cheap set to get this done. Inside mic should work for depth, I haven't used one in so long I forgot I had them. I don't have gauge blocks and probably don't need that level of accuracy anyway

[Toolguy]

Use an inside spring caliper to measure the diameter. Expand it so it just touches the widest point, compress and pull it out, let it expand again and measure it with a mike or dial/digital caliper.
For the width, you could buy a $15 digital caliper and cut off the outside jaws to fit it in the tube.

https://www.ebay.com/itm/15218000550...sAAOSwdzVXlTwM

[chipmaker4130]

On a 1/4" wide groove an inside mic is what I use. Regarding width you should be able to get close enough for hydraulic work with the back end of your calipers. This is assuming the groove is near the open end of the cylinder. If you need tighter width measurements, gauge blocks.

[Captain K]

How do you measure to depth and width of an inside groove? I am building a hydraulic cylinder gland and need to measure the seal groove. 2 3/4" bore, groove will be say 3" diameter and 1/4" wide. Obviously no place for sloppy work so how do I get it right the first time? This is a one time deal so would rather not buy too many expensive tools to complete it.