Doing the trig to machine some joint holders and form tools.

**snoopdog6502** · 08-07-2019, 02:39 PM

Being a 1 in 10 taper I get 5.711 degrees from center line.

If im going to set the compound on my lathe I figure I better make male and female, brass and graphite joint forming tools with an air passage.

Does my figure 5.711 degree sound right? Does anyone have some charts with the actual dimensions of standard joints.?
Most of the charts I found are arbitrary as hell. Im shooting for the gnats ass so my tools will make joints that fit others perfectly.

My trainee is wanting to make rigs and buying clear joints is not in the plan at all, sure as hell will not put a clear joint on a colored piece.

I have stock ordered for graphite 14mm to start. will do some 10MM and later some 19 mm.

Any information would be helpful.

**Subduction** · 08-07-2019, 03:43 PM

http://www.bacto.com.au/glass-conical-joint-sizes/

Looking at 24/29 size: 24.0 - 21.1 = 2.9mm diameter difference over a distance of 29mm

The tangent would be 2.9/2 divided by 29 = 0.05

Arctan of 0.05 = 2.862 degrees

[I think--but I haven't been in a machine shop for twenty years]

**snoopdog6502** · 08-07-2019, 04:00 PM

Originally Posted by Subduction

http://www.bacto.com.au/glass-conical-joint-sizes/

Looking at 24/29 size: 24.0 - 21.1 = 2.9mm diameter difference over a distance of 29mm

The tangent would be 2.9/2 divided by 29 = 0.05

Arctan of 0.05 = 2.862 degrees

[I think--but I haven't been in a machine shop for twenty years]

opps sorry reade it wrong, its still not detailed enough.

I measured a quartz 14 mm.

**snoopdog6502** · 08-07-2019, 07:31 PM

I think to start I will machine a long tapered reamer to dial in the angle to a high degree of accuracy. Then make to tools.
I am converting a measurements to thousands of an inch as my micrometers are in .0001
Max resolution.

**Cerberus** · 08-08-2019, 09:18 AM

Snoop I made sets of male and female 10 and 14mm joint tools. I measured some male joints on my optical comparator to get the angles and will confirm 5.71 degrees per side (11.42degrees included) on the joints I measured. The difference of .01 degrees from calculations is negligible and the difference falls within tolerance allowance and batch to batch variation. I ended up setting the small angle attachement on my lathe as close as I could get it then going back and forth to comparator and gently adjusting the angle slide after taking a cut to match the taper. I also used purchased joints for a mechanical "gage" check to confirm fit. Locked it down and made all the tools back to back so all tools had exactly the same taper. Using the rear taper attachment I could use a boring bar for the male holders, not sure if that is an option on your machine. If you're not going to make a bunch of tools you won't even need to harden your reamer, a half round style would probably work just fine if you don't want to spend the time to cut flutes.

Considering tolerances on matching small angle tapers you'll never get 100% full contact on the joints no matter what, so get as close as you can and you'll be good. Glass doesn't allow ANY deformation for a mechanical lock (like you get with softer material like metal) so at best you get line contact for a seal at either end of the joint which is fine for this application. The first use will seal with water or oil.
If you have the time and materials and you're lathe is set up I would suggest turning out a bunch of lap plugs so you can grind your joints to perfection! Might even be able to sell a few laps to cover your costs, hint, hint.
Shoot me a dm or email, i'll hook you up with some info.

**Subduction** · 08-08-2019, 01:03 PM

I can't argue with the physical reality of a comparator but (as of now) I stand by my theoretical answer of the included angle being 5.724 degrees (5 deg, 43 minutes).
http://www.magafor.com/841/uk.htm
https://www.geekworldz.com/2016/02/h...per-ratio.html

Click image for larger version.

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**AxisWolf** · 08-08-2019, 03:59 PM

Awesome work guys!

**Super Phunk** · 08-11-2019, 06:03 AM

Why not just buy them? How much time and money in lost glass blowing and supplies is it going to cost to make them???

**hashmasta-kut** · 08-11-2019, 10:26 AM

Colored ones. Worked ones. All handmade. Once you get good at making them its pretty quick.

Or do you mean the tools? Ya i bought tools.

**Swim** · 08-11-2019, 11:20 PM

I run them quick as fuck on the lathe once i am in the zone, and I get a thicker prettier joint

**snoopdog6502** · 08-11-2019, 11:38 PM

a foot of 5/8 graphite rod cost me 7 bucks, machine time will be very fast as it cuts like bread. I will get 6-8 tool ends for almost nothing.

I could buy the tools but fuck that, its not hard to make them.

**lsspam** · 08-12-2019, 02:04 PM

The standard specification for international tapered joints is ASTM E676. The Batco link posted is for table 4 "International-Length Taper-Ground Joints" which have a 1:10 taper but a different ground length. Tables 1, 2, and 3 are for full, medium, and short length joints. You need to know which length joints you are trying to mate to.

Setting your compound to 2.86 ± 0.01 will get you close enough. To determine the final taper for interchangeably you need a driving tool either hard steel, diamond impregnated, or an old school tin lap. Depending on the desired finished you will grid with different grits of carborundum.