How to use a caliper

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mmoncur

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So I have a decent digital caliper and I decided to try it when making pens. How exactly do I use it?

I assume I should measure the pen component (i.e. nib) at the widest part, then measure the corresponding end of the pen. Should the readings be identical? Should the pen be slightly larger? Is there a formula?

Previously I've been turning a hair proud of the bushing, rounding the sharp corners, and I've had a pretty good fit. But when I tried the caliper on a slimline I'm working on there's a huge difference (well, half a millimeter).

Anyway, for those who use calipers, what's your process?

Thanks in advance!
 
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I turn to about .020" over and sand the rest of the way so I have an exact match to the hardware.. You can deduct for a CA finish if you apply it real thick but I don't. It's better to have the the blank a few thou bigger than the hardware, if the blank is smaller you can feel it more. That being said, if you can get them both the same that would be ideal, but that's not easy and it all depends how much time you want to spend on it.

One tip...If you have one of those plastic calipers, don't use it on a spinning blank....DAMHIKT!:biggrin:
 
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rherrell said:
That being said, if you can get them both the same that would be idea
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But if it's a wood blank, remember it can change a little with the environment. Today's "the same" can be tomorrow's "slightly over- or underturned".

Overturned (pen components proud of the barrels) is worse than underturned, so I prefer to err on the side of barrels being bigger. Slightly rounding the corners helps it feel and look the best.

With something stable like plastic, hitting the target size exactly with crisp corners is ideal.
 
One tip I have been using when checking the measurement with the blank mounted between centers (or on a mandrel) I find it hard to see the measurement without pulling the calipers away and worry that I may be moving them ever so slightly in the process ... so what I have been doing is when I have the measurement I hit the reset button then pull it away and close the calipers. This results in the measurement as a negative number. I know some take a reading of the bushings and then hit reset, then turn till they hit zero indicating a match to the bushings.
 
:search: Sometimes the fittings are not the same size as the bushings. Always measure the fittings and use the bushings as a turn close to point. Bushings also wear down with use. Some pen kits have a different size fitting from one end of the tube to the other. HP has a spring loaded calipers so you don't have to lock your settings. Works great if you set your regular calpers to the exact size, and then use the spring loaded one to check as you reduce the blank. Switch to inches when you are looking for drill sizes and dowload a drill size chart from the library. You might want to also chech into HPs 115 piece drill set. Watch for it to go on sale, and use the 20% off cupon. Will give you much more accurate size holes for your tubes. Jim S
 
I use a dial caliper rather than a digital because it has a nice lock feature to lock in the measurement.

I'll usually measure the component and then add .01-.02 so it's a loose fit over the component. Then I'll turn the blank to match and by the time I sand it's pretty much spot on. As mentioned, you're better to be a touch over than under. You can always put a slight round over on an overturned blank and it will feel just fine to your fingers.

If I'm doing a CA finish, I'll turn to the exact measurement and by the time I sand and apply the finish, I'm typically right where I want to be.
 
Thanks everyone! I guess I need to bite the bullet and start switching to TBC, the bushings are just in the way. I just like slimlines so I keep using a mandrel with those.

P.S. The caliper was right, the pen I was working on was indeed proud of the components. I always round the edges so it looked OK, but I'll try to get closer next time...
 
TIP: If you have a digital caliper, put the caliper on the fitting, then press the zero button. Now when you put the caliper on the blank, it will show the amount you need to take off for an exact fit. I usually turn down to about .008" to .012" oversize, then sand off the rest. A thin CA finish makes a perfect fit. On wood pens, I like a satin finish, so after the CA, I hit the blank with some non metallic abrasive for a nice wood feeling surface.
 
I've got a strange question. I've been TBC for a couple weeks. I measure with Digital Calipers to try to match the components. I'm finding that the measurements are not the same when I have it on the lathe between bushings as when I take it off. Taken off the diameter is actually larger than when it was on. I've seen this with a variety of wood. I'm working in a moist basement, but I can't see how that would make a difference between on and off the lathe. The only other thought I had was that maybe the blanks expand after cooling? Am I crazy???
 
Could it be that you can't get at it when it's on the lathe to get an accurate measurement ... Or maybe like, I said in my other post, in the process of pulling it a away to read maybe it's moving ???
 
Lenny said:
Could it be that you can't get at it when it's on the lathe to get an accurate measurement ... Or maybe like, I said in my other post, in the process of pulling it a away to read maybe it's moving ???
Click to expand...

No, it can't be either of those things because it is actually bigger when it comes off the lathe.
 
plantman said:
:search: You might want to also chech into HPs 115 piece drill set. Watch for it to go on sale, and use the 20% off cupon. Will give you much more accurate size holes for your tubes. Jim S
Click to expand...

I really dislike acronyms. -- So who/what is HP? And where do you the referenced coupon?
 
gallianp said:
plantman said:
:search: You might want to also chech into HPs 115 piece drill set. Watch for it to go on sale, and use the 20% off cupon. Will give you much more accurate size holes for your tubes. Jim S
Click to expand...

I really dislike acronyms. -- So who/what is HP? And where do you the referenced coupon?
Click to expand...

Acronyms are more difficult when they are mis-spelt!!

I believe he means Harbor Freight ---HP??? or Hewlett Packard----HF???

Merry Christmas, one and all!!:biggrin::biggrin::biggrin:
 
I never like the readings I get when measuring on the lathe. I remove the blank and measure. Yes it is more work but I like the results I get. Also in you have a taper to the blank you have to be careful to just nip the very end with the caliper so you are measuring the very end that comes in contact with the metal parts. Bushings are only to get you close.
 
mpex said:
Am I crazy???
Click to expand...

You might be, and it might help in some cases but not with TBC! :biggrin:
I sometimes think similar things are happening and then I realize that I had the calipers either on an angle or too far up where there seems to be a step in the caliper jaws. Never could figure out why they make em that way!:rolleyes:
 
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