Best way to measure bores while piece is in milling vise?

jlsmithseven

jlsmithseven

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Hi Guys
Starting my first boring holes project. I usually just flip my caliper set backwards and measure the inside of the holes this way, but I've been told that telescoping gauges are better for the job.
However, when my boring tool is directly above the piece, it's hard to get a measurement with any tool. Am I supposed to move the piece away from the collet to measure it? Even with a DRO, this will mess up my location won't it? What's the best way to measure bores while I'm still machining them? Thank you!
Justin
 
If you have enough room in Z, lift the head so you can access the bore with a telescoping gage. Another option is an inside micrometer; these typically measure in the thousandths (0.001"). These are vastly more accurate to use than the inside jaws of a dial caliper. Bore micrometers can work well because the handle can be tilted over to the side while still getting a reliable reading. Bore gauges normally need to be used vertically so, again, it depends on how much room you can make in Z.

I use all of these but which one depends on the project. For convenience, I think an inside mic would be the best bet. They normally are available on ebay, like this one:http://www.ebay.com/itm/MITUTOYO-MODEL-145-193-2-TO-1-0-INSIDE-MICROMETER-IN-THE-BOX-/351962992025
 
Justin,
Depending on the accuracy you require your calipers might be just fine. A bit of info on your machine would help too. Presumably as your boring holes you have some Z travel. Any reason you cant increase the z clearance to fit in a inside mic or a bore gauge, if necessary? Just remember on small dia holes your caliper can give a false undersize reading regardless

Cheers Phil
 
Thanks for the inside mic recommendation, that looks pretty cool. I can't really raise the head, I guess I could lower the handle every time I wanted to make a measurement, but that's a lot of time and effort wasted. Right now my tolerances are + or - .003 so I think I'll be OK with what I'm doing, I just wanted to see what else was out there!
 
if the holes are in the range of any gage pin you might have they would be ideal
 
If the bore is large enough, you can often rotate the boring head to get the cutter to the rear and make your measurement in front of it with snap gauges or an inside mic. If the bore is small or I need to use a dial bore gauge I move the part forward and rely on the dro to get back to the same spot.

Greg
 
Unless your location is super critical and you are very very close to size, there should be no reason to distrust your DRO. It should bring you back within 0.0005, but only if you go through some testing could you get to trust that. You should try it at least. Make a pass, dial off, dial back to location and then sweep the hole to see how close it came back. On my bp clone, I have a Mit 0.0002 resolution DRO and it seems to repeat rather well. I generally move away from the spindle if I can't get the headroom to measure without it. I find that on the work I do that if the hole is large enough where I prefer to bore it rather than ream it the location is not so critical that I miss it when I do dial away and check the size.

You could also get a good indicator, either test or drop and park it on the axis that makes the most sense, and use it as well as your DRO to check your re-position. You may find that moving just one axis will allow you to get in and measure.

The point is well taken regarding using calipers for bore work, if you are dealing with tight tolerances. They are not the optimum choice. If you already have the OD mic range you are working in, then invest in some quality telescoping gages. I prefer Mits to all on that, firmly. They have a smoother action and a little more reach than others. Just don't cheap out on them. You will regret it. And learn to use them. Practice on some known sizes until you get consistent reading. There is a little art to getting it right using them.
 
I'll second Tony's reference to cheap telescopic gauges. I bought a Chinese set, they were rough and had no feel to them. Bought a set of Starret and in an evil mood gave the Chinese ones to a friend.

Greg
 
Even the Brown&Sharpe telescoping gages are inferior. What's the point in buying a cheap set of these gages coupled with inaccurate micrometers?
For me, it's not always a question of trying to hit tenths every time but knowing how far off you are to begin with so that I can strive for the utmost in accuracy.
I hear this all the time at work, "we don't need to buy such accurate tools, we're not going for tight tolerances". OK, but how do you know how far off you are?
Just my humble opinion. :)
 
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