Caliper technique/tips for final sizing of blank?

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Dave Turner

Dave Turner

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Joined
Jul 23, 2010
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Sylvania, Ohio
I find that the bushings are fine for rough sizing of the blanks as you turn them down, but are not accurate enough to give a perfect fit to the pen parts. I've been measuring the actual pen parts with a digital caliper and then turning the blank ends to that diameter using the caliper. After rough turning using the bushings so its just proud of the bushings, I remove the bushings and switch to "cone" adapters on the mandrel (for now will switch to between centers once I get my drive attachment).

My problem is that it takes a long time to get the diameter perfect. Take a little off, turn off the lathe, measure with the calipers, turn on the lathe, take a little more off, turn off the lathe, measure again .... and repeat ..... and repeat again as needed ...... I've been reluctant to measure with the lathe running for fear of a catch, or at least major scratching that would require sanding below my desired diameter.

My question is, what techniques or tips/tricks do others use to get their diameters perfect? Do you modify your caliper in some way with grinding so you can set it to the desired diameter and just let it rest against the blank as you turn it? Thanks for any suggestions.
 
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Use the bushings to turn the pen. But, use the bushings for a reference only. Turn close to the bushing then start using calipers. It goes much faster for me this say and less measuring.

Do a good turn daily!
Don

Dave Turner said:
I find that the bushings are fine for rough sizing of the blanks as you turn them down, but are not accurate enough to give a perfect fit to the pen parts. I've been measuring the actual pen parts with a digital caliper and then turning the blank ends to that diameter using the caliper. I do this without the bushings in place using "cone" adapters on the mandrel for now (will switch to between centers once I get my drive attachment).

My problem is that it takes a long time to get the diameter perfect. Take a little off, turn off the lathe, measure with the calipers, turn on the lathe, take a little more off, turn off the lathe, measure again .... and repeat ..... and repeat again as needed ...... I've been reluctant to measure with the lathe running for fear of a catch, or at least major scratching that would require sanding below my desired diameter.

My question is, what techniques or tips/tricks do others use to get their diameters perfect? Do you modify your caliper in some way with grinding so you can set it to the desired diameter and just let it rest against the blank as you turn it? Thanks for any suggestions.
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I do what you do, but as I do more i'm gettign a better feel and it is startign to take less time. Measure your bushing compared to the parts. May save a little time if you know if your target is a bit bigger or smaller than the bushings as you can get closer before removing them.
 
lol... The "efficiency of time" side of my brain has considered using calipers on a turning lathe, but luckily the "I like having 10 fingers and no bleeding gash in my forehead" part of my brain has always won the debate. I cannot think of any modification that could be made to a set of calipers to make that safe, let alone have it remain anywhere near accurate. Ball bearings or little wheels would be the only contact method I could think of. A laser should be able to do it, but the calibration would be almost as much of a nightmare as the price...

I do just what you do, cut, stop, measure, cut, stop, measure..I'm getting better at judging about how much is safe to take off before checking again (but I do over cut every so often, so I've gotten good at the super-deep CA finish...) I find that things can be very consistent with tools, but when you get to sandpaper, you need to be aware of your materials, as some harder woods and acrylics will take forever to get .005 off with 400 grit, softer woods will drop .010 pretty quickly with the same grit.
 
if you do not mind doing this, you can put a radius on the inside ends of the calipers so there is no point to stick out.
Then set the calipers to a few thousands above what you want to be, you can then set them over the end of the blank, and even move them off to the side over your bushing.
Once the caliper slips over a spinning blank, you should be right on, may a little large.

same trick that is used for making tenons and sizing spindle work that are on the smaller side.
 
Truth be told, I'm glad that all of you turn with calipers. I've never ventured there. Perhaps it shows in my pens and you are each too kind to comment.
 
DCBluesman said:
Truth be told, I'm glad that all of you turn with calipers. I've never ventured there. Perhaps it shows in my pens and you are each too kind to comment.
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I would never dare assume that. There are people out there who can to better than me by eye than I can do with the best tools. I watched a video series of Sam Maloof and was amazed at what he does - and his work speaks for itself.
 
I don`t use calipers. for the life of me i can never get the same measurement twice with any certainty. When there are two different sizes for the top and bottom of one barrel i get mixed up. One time i thought i solved it and i used two sets of calipers and i got lost as to witch was witch in the sawdust.
 
I compare bushing sie & parts size. I have found bushings to be right on, so I turn to them. Any difference I do as you. Check-turn-check-turn. Sometime this can be a lot of trouble cause I have a problem with being shakey as heck so more than one measurement is needed. I never get in a hurry to finish a pen. Whatever time it takes, so be it. As long as I've done my best.
 
soligen said:
I would never dare assume that. There are people out there who can to better than me by eye than I can do with the best tools. I watched a video series of Sam Maloof and was amazed at what he does - and his work speaks for itself.
Click to expand...

I was going to say the same thing... Calipers appease my brain's need for measurement and precision, but I have seen here and in person that it is not necessary in order to get a great pen, but it makes me appreciate the craftsmanship of those who can do it without letting technology and math get in the way.

As for getting the same measurement twice, I have that all the time too, but I try to keep in perspective that a variance of a few .001's is not a big deal, and I take pains to be sure I'm measuring as close to the end of the barrel as possible
 
calipers

My calipers have rounded ends.
I measure while the piece is spinning.
I've always found that I am more able to determine a flaw than someone else.
Something readily noticeable is an error, not a flaw. (My definition)
Being over 1/1000th is not a flaw. It might not be perfect but it is not a flaw. Hand made pens are more desireable because they are not all exactly the same.
Just one persons thoughts.

Lee
 
One good tip with digital calipers is to put the calipers on the fitting and press the "zero" (origin) button on the caliper. Your caliper will now read how much you are oversize. This helps because you know how much you need to take off.
 
I use my digitals only for measuring the bushings. If they're off then my 40 year old screw calipers come out. I've smoothed and polished the tips so there's no risk of damaging the blank while checking on a lathe spinning at 2000rpm. Let alone a catch and succeeding impalement.
 
If you have to choose between overspun and underspun, over wins every time, especially if you have a little run-out causing your blank to be a touch out of round. If it is way out of round..that's not good, but my point is that if you spin the blank a thousandths oversized and then take just a quick swipe of the edges with sandpaper before polishing the blank up, then you won't feel any transition between the parts and the blank. If the blank is undersized, you will feel the sharp edges of the parts. If it is slightly and I mean really slightly out of round, because you turned it just a smidgen oversized and then broke the edge on the blank..you won't have one side where you feel parts and the next side where you feel the blank..it will just blend together in the hands. I'm talking about just breaking the edge of the blank, not rounding the heck out of them of course. My pens are rarely out of round too...but hey, everyone has a bad day. I use this technique on all my pens, I feel nothing between the barrels and the parts, just a smooth even transition.
 
I measure with the lathe off. If there's a taper, you want to make sure that you're using the narrow edge of the caliper right at the end. If you're not paying attention, you can easily measure futher towards the middle than you are concerned about, and that throws things off.

Also, I reccomend using plastic jawed calipers. They're just as accurate as steel, if you take care of them, and they won't marr your hardware or the finish on the blank.
 
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