Measurement and aluminum question

[workinforwood]

I was wondering if anyone can accurately measure the inside diameter of the 2 tubes used in the JR Statesman II, which I think is the same as the Gent II. I'm ordering some aluminum and would like to have them drill it out to that diameter so that I don't even need to use the tubes. My calipers are plastic, unreliable and can't honestly say I know how to read them anyhow. I use them to measure and match only, so if one piece says 49, the other needs to be 49, hahahha. Then I also say a prayer.

Thank you guys so much. If two different skilled people can take the same measurements, all the better.

Also...is there a specific grade of aluminum I should be asking for?

 

[Firefyter-emt]

The better bet would be to measure the hardware and deduct a hair off of it for a good fit. Tube measurements are tricky to get perfect even with good calipers like I have.

 

[skiprat]

I don't know those measurements, but I would not measure them anyway.
I would measure the outside diameter of the parts that are going to be pressed in. The parts normally have a leading edge before the part needs to be pressed. Thats the diameter I use.

The ali I use is often unknown scrap but I believe the best stuff is the type that has a 6 as the first of four digits. eg 6105.

However, I have used cheap ali tube from a DIY store and although it does scratch, it's really not bad considering the pen lives in my toolbox. Good luck

 

[johnnycnc]

Hiya,Jeff I'm guessing you have something similar
to this cigar set in mind?

<br />

<br />
6061 is a very common,popular aluminum grade.
These are prototypes,have not had time to turn yet.
First,I squared the ends and made them same length as tubes.
No pen milling,or end squaring needed.
There is a hole drilled thru,almost as big as the
fittings,then I cnc machine a precision bore for the
fittings.these will have .0005 per side press fit.
No tubes.
I can get you measurements,for your set,but it kind of depends
on your idea of fit for your kit parts.I would recommend
.0005 per side press fit.And likely a drill won't produce
exactly the size you want to a close tolerance.Maybe,but not
likely.[]
Hope this helps.

 

[Rifleman1776]

Decent calipers are not expensive and are a good investment.
I would measure several ways. One, measure the ID. Two, measure the OD then the thickness of the metal and subtract. And, with a large set of drill bits, just keep trying until you get one too large and use the next smaller size as a guide. Or, contact the supplier and ask.

 

[Randy_]

The other problem you have is that a correct press fit in a brass tube will not be the same as one in an aluminum rod. The brass is soft and thin and will stretch a little when you press the hardware in. You won't have the same stretch (less) with the aluminum so the fit will have to be slightly looser.

You might want to email Paul in OKC (a professional machinist) and ask him what a proper fit should be. I'm guessing the fit should about 0.0005" under. I'm also guessing that there is that much variation among the hardware and most people are not going to be able th measure that closely anyway.

When you are looking at that kind of precision, the usual method is to drill or bore a little under size and then ream to the exact size. I'm again going to guess that the guy who drills or bores your aluminum is going to want to have the actual hardware in hand so he can measure it up himself.

Possibly, this is a situation where you get a looser fit and use an adhesive of some sort??

 

[workinforwood]

Right, just hunker down and make the hour drive sounds like the right thing to do, so they can measure the parts themselves and cnc the hole. Thankx guys []

 

[johnnycnc]

Jeff, I'm sorry if you took offense to my reply
in some way.

Originally posted by workinforwood
<br />Right, just hunker down and make the hour drive sounds like the right thing to do, so they can measure the parts themselves and cnc the hole. Thankx guys []

 

[workinforwood]

Not sure why you'd consider my reply to mean that I am offended by something. What I'm reading as good advice is to let the mill person do his own measuring...and that sounds like a smart idea. I was being lazy because the aluminum place is an hour away, but laziness is probably a bad idea. Better to make an order in person that on the phone.

Now...if you (John)have aluminum and a cnc and the JR statesmen 2 pen kit on hand and want to make what I need, I'd definitely take that road, assuming the price was affordable. I know at the factory they can blow it out quick, since this is the type of stuff they do all day long...but why drive if you don't have to. While your at it, make a couple for those artist pencils from CSUSA that take the 5.5 mil lead. The single barrel ones, I have a guy that would buy the statesman and the pencil in aluminum. []

 

[Mudder]

Your first two replies are very good ones and the cheapest and easiest way to go. The third reply will be the most accurate and the easiest for me since I work Quality control in a machine shop. The trouble with measuring the inside of a brass tube is threefold. First off, and I know I'm going to get arguments about this, a caliper is only good to +/- .001" according to ISO standards. While perfectly acceptable for most woodworking tasks I would question it's usefulness in this case. The second and third reason are as follows. The brass tube can and and probably will flex while measuring to be slightly out of round throwing off your reading and the jaws of the caliper are flat. I know that the flats are very small but in my field we routinely measure to .0001 (one ten-thousandth) and under.



I have added an illustration that I hope will make my point a little more clear.

Lets suppose your brass tube is 1/4" inside diameter (.250") and the flats of your vernier are 1/32" (.032"). You can see where the edges of the flat contact the tube but leave a gap. In this case the gap is .001" per side so in theory your tube that is actually .250" in diameter will read .248" on your caliper. (In truth it should read slightly less that .248" because the contact edges of the caliper are offset from each other a small amount for clearance but that is for another discussion.)

A decent micrometer capable of measurements to .0001" is available for less than $10.00 here:

http://littlemachineshop.com/products/product_view.php?ProductID=2877

(OK, with shipping it will be a little more than $10.00 but you can get my point) And for penturning you can find as many uses for it as a caliper.





I do not have a JR Statesman II of I would make the measurements for you.

Hope this helps someone.

 

[johnnycnc]

Jeff,I was just making sure,about my earlier reply.
(driving an hour sounds like no fun).
Hey,I'm on a quick break at work now,but I will PM you later
when I get home.I think we can work something out.[]

 

[CrazyBear]

I tried a similar ploy when I lost the brass tubes for a slimline.
I picked up some 8mm Aluminum tubing . Hole was too small to either accept parts or mandrel. 6m bit just slid into the tube. 6.5mm bit made the hole too large. DoHhhh! So I will just have to wait till my new pen kits arrive[][][]