Plug gauge

[Gordon]

Is there any source for short lengths of ground and polished shafting? I am thinking just a couple of inches of the common cylinder sizes .625, .5, .875, 1.0, 1.125, 1.25 etc. to use as a plug gauge. I am finding that telescoping gauges are not too dependable and only measure at that point in the bore. At another point the diameter may be different than that. I realize that plug gauges are available but the cost is more than the small shop can justify. I have made a few from steel shaft but that is a time consuming. I suppose that at some point I will end up with all of the common sizes if I keep making them.

 

[Asm109]

You can buy dowel pins from McMaster Carr. They come about .0002 inches over nominal.

 

[BaronJ]

Hi Gordon, Guys,

For holes 13 mm and smaller, I tend to use drill shanks or unthreaded slot drill shanks. I have sets of Dormer drills in tenths of a mm steps. For larger I use bore gauges and/or calipers and mic them.

This is a 35 mm bore.

When I was making my front and rear tool posts.

 

[nautilus29]

I look on ebay, and I've pick up some common sizes there. Every once in awhile you can find a couple for a decent price.

 

[Gordon]

I have tried ebay but I have not found anything. The local facebook marketplace has an ad for someone nearby who has about 2000 gages but he does not answer his email and he does not list prices. Dowel pins are too expensive in the larger sizes and the smaller sizes I can use things like end mill shank and drill bits. I will keep looking for a reasonable solution.

I have found that using telescoping gages does not give a consistent result. It can be to size at one end and off size at a different point. Either my poor skills or less likely my machine.

 

[nautilus29]

There's definitely a feel to telescoping gages, and you are right, if your hole isn't perfect you are only getting one reading. Usually when I'm using them I check the hole in multiple places to see if there is any variance. A lot of times you want to see if the hole isn't perfectly round and a pin won't show you that as easily. Especially if the hole is bigger in the back than it is in the front.

What process(es) are you doing that you are trying to mic? Boring, reaming drilling? On a lathe or mill? You could buy a lot of used end mills and use the shank of the end mill as your standard. I'm not sure about pricing but buying drill blanks may also be an option.

 

[IanN]

Is there any source for short lengths of ground and polished shafting? I am thinking just a couple of inches of the common cylinder sizes .625, .5, .875, 1.0, 1.125, 1.25 etc. to use as a plug gauge. I am finding that telescoping gauges are not too dependable and only measure at that point in the bore. At another point the diameter may be different than that. I realize that plug gauges are available but the cost is more than the small shop can justify. I have made a few from steel shaft but that is a time consuming. I suppose that at some point I will end up with all of the common sizes if I keep making them.

Hi Gordon,

Ok - I admit I'm a bit confused by your post: You do not want to pay for commercial gauges or a set of dowel pins (which, I agree, are very expensive if you only ever use them half a dozen times) and you do not want to invest the time in making them yourself......

Without knowing what you are trying to do, and what tolerance you are working to, it is very difficult to make any useful suggestions.

As Nautilus has pointed out, a plug gauge will only tell you that the narrowest part of the hole is bigger than the widest part of the gauge - a plug gauge is a quick go-nogo test used in production to check parts as they roll off the production line

If you want to measure, test or check for ovality and taper you need to measure. Telescoping "Tee" gauges are too big for some of what you are trying to assess and "expanding ball-type" gauges are more appropriate - and you will need to invest some time in learning how to use them.

So what are you actually trying to do?
What level of accuracy and precision do you need to achieve?

All the best,
Ian

 

[IanN]

Hi Gordon,

I meant to include a link to my particular weapon-of-choice for checking bores - it is home-made and I've recently mentioned it in another thread so I'll include a link rather than re-post:

https://www.homemodelenginemachinis...-core-in-cyl-casting.32901/page-2#post-354664
All the best,
Ian