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#5813803 - 07/01/15 05:53 PM Barrel Threading Concentricity Tolerance ????
dredd Offline
Tracker

Registered: 04/26/10
Posts: 908
Loc: Dallas / Fort Worth Area
I have a Suppressor coming in within the next month (I Hope).
I am going to need two Barrels threaded. ( 5/8-24 )

I stopped by Alamo Precision today to discuss it.
First time I have been there.

The gentleman at the counter said that he can hold "Ten Thousandths on Center". ( 0.010 )

I am not a Gun, Barrel or Suppressor Manufacturer, but that sounds "loose" to me.
Granted, that is 0.005 per side, but that still seems like quite a bit coming from a custom shop.
I repeat... I do not thread Barrels, so I do not know.

I did try to Google it, but didn't really find what I was after. (Probably poor searching skills)

Does anybody have any "hard" numbers that one should expect their Barrel/Thread Concentricity to be held to?

Thanks!




Barrel Threading Concentricity Tolerance

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#5813805 - 07/01/15 05:54 PM Re: Barrel Threading Concentricity Tolerance ???? [Re: dredd]
Cleric Offline
Veteran Tracker

Registered: 03/11/12
Posts: 2759
that is a hundred thous

ten thous .0001

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#5813808 - 07/01/15 05:56 PM Re: Barrel Threading Concentricity Tolerance ???? [Re: dredd]
Cleric Offline
Veteran Tracker

Registered: 03/11/12
Posts: 2759
more detail...

Machinist Talk
In general conversations or math class you may hear numbers spoken one way, in a Machine Shop, you may hear the same number described differently for example:

Keep in mind for the following:
In math class everything is based on 1.0
In a Machine Shop using Inch measurements, everything is based on .001" (one thousandths of an inch)

So, how would we say the following?

0.1000
in math class = "one tenth"
in a machine shop = "one hundred thousandths
WHY? because if everything in a machine shop is based on .001 then there are 100 - "thousandths" of an inch

.0100
in math class = "one hundredths"
in a machine shop = "Ten thousandths"

.0010
in math class = "one thousandths"
in a machine shop = "one thousandths" or "one thou"

.0001
in math class = "one ten-thousandths"
in a machine shop = "one tenth"
WHY? because if everything in a machine shop is based on .001 then there is 1/10th of one thousandths of an inch

.00001
in math class = "one hundred-thousandths"
in a machine shop = "Ten Millionths"

Machine Shop examples:
12.3456 = Twelve inches, Three hundred forty-five thousandths and six tenths

0.12345 = One Hundred Twenty-Three Thousandths, Four Tenths and Fifty Millionths

0.5430 = Five Hundred Forty-Three Thousandths

0.0123 = Twelve Thousandths and Three Tenths

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#5813819 - 07/01/15 06:05 PM Re: Barrel Threading Concentricity Tolerance ???? [Re: dredd]
dredd Offline
Tracker

Registered: 04/26/10
Posts: 908
Loc: Dallas / Fort Worth Area
So, if I understand what you are trying to say...

You are telling me that he can hold 0.0001 ????

The odds of that being accomplished on an engine lathe with a steady rest are..... way out there, to say the least.
I won't say impossible, but..... darn near.

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#5813862 - 07/01/15 06:24 PM Re: Barrel Threading Concentricity Tolerance ???? [Re: dredd]
Cleric Offline
Veteran Tracker

Registered: 03/11/12
Posts: 2759
With todays lathe people can run far higher tolerances.

Get a good 4 jaw chuck, mount it right, have a good balanced lathe and its doable easily.

I was running a table top lathe and holding .001 so with better equipment would be no problem

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#5813907 - 07/01/15 06:39 PM Re: Barrel Threading Concentricity Tolerance ???? [Re: dredd]
FiremanJG Online   content
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Registered: 12/16/08
Posts: 19171
Loc: Wolfe City, TX
My gunsmith bud centers to five ten thousandths. Shank and muzzle end alike.
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#5814182 - 07/01/15 09:16 PM Re: Barrel Threading Concentricity Tolerance ???? [Re: dredd]
patriot07 Online   content
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Registered: 11/06/11
Posts: 1277
Loc: Royse City, TX
.010 (+/- .005) should be easy

.005 (+/- .0025) should be do-able for a good machinist on a good machine

Anything tighter than that would have to be done with really good tools on a really good machine by a really good machinst, and it's not going to get a whole lot tighter than that.

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#5814390 - 07/02/15 05:17 AM Re: Barrel Threading Concentricity Tolerance ???? [Re: patriot07]
dredd Offline
Tracker

Registered: 04/26/10
Posts: 908
Loc: Dallas / Fort Worth Area
Originally Posted By: patriot07
.010 (+/- .005) should be easy

.005 (+/- .0025) should be do-able for a good machinist on a good machine

Anything tighter than that would have to be done with really good tools on a really good machine by a really good machinst, and it's not going to get a whole lot tighter than that.


I agree with your post.

I am curious to know what the "world of guns" considers an acceptable tolerance/result.

Is .010 sloppy, or actually tighter than it needs to be for that particular function?

Thanks for the replies.

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#5814454 - 07/02/15 07:12 AM Re: Barrel Threading Concentricity Tolerance ???? [Re: dredd]
pertnear Online   content
Bird Dog

Registered: 12/31/14
Posts: 295
Loc: Kingsland, TX
I'm definitely no expert here, but do extremely close tolerances really matter? I get that we don't want the bullet to touch the sides of a long suppressor, but what is the size of the hole down middle of the suppressor? The bullet is traveling ahead of the hot gases, so long as there is plenty of clearance it doesn't seem too important. Please educate me.

TIA
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#5814783 - 07/02/15 11:10 AM Re: Barrel Threading Concentricity Tolerance ???? [Re: pertnear]
DallasShootingSupplies Offline


Registered: 05/21/09
Posts: 4136
.001 is perfectly acceptable. Mine are typically .0005 when I start threading.

.003-.006 likely won't harm the can but will harm accuracy, with can.

I have fixed several that were acting strange with .005ish off center, that other gunsmiths did. Several where THF guys who came to me with erradic groups with cans.

Anything .007-up can cause a baffle strike.

Threading on inside bore is absolutely crucial, lots of pics and vids on my forum post and FB showing how bad off center bores are from the factory. Most recent was an coharie MP5 that was about 25 thousandths off.


Edited by DallasShootingSupplies (07/02/15 11:54 AM)
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#5815826 - 07/03/15 12:13 AM Re: Barrel Threading Concentricity Tolerance ???? [Re: dredd]
Stick1 Offline
Light Foot

Registered: 08/19/09
Posts: 21
dredd,

Not sure who you talked to up front, but to clarify, we indicate off the bore to the nearest "tenth" (.0001). It would take a machine beyond special to actually hold that tolerance. We will usually end up around .0005 or less TIR on barrel threads. Hope this clears things up.

-Robert

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#5816118 - 07/03/15 10:35 AM Re: Barrel Threading Concentricity Tolerance ???? [Re: dredd]
dredd Offline
Tracker

Registered: 04/26/10
Posts: 908
Loc: Dallas / Fort Worth Area
Robert,

I did not get the gentleman's name.
He mentioned that the Boss had left and he was watching the store front.

I appreciate your reply. It definitely cleared things up. :-)

BTW... I think your store front looked very "clean".
More items than I thought you would have and well laid out.

I'll stop back by when my suppressor comes in.

Thanks,
Brett

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#5819367 - 07/06/15 09:15 AM Re: Barrel Threading Concentricity Tolerance ???? [Re: dredd]
ccoker Offline
Veteran Tracker

Registered: 09/17/09
Posts: 3374
I don't trust most gunsmith to do threading work.
I do trust Morgan at Dallas Shooting Supplies.
He's fast, does it right and his prices are VERY reasonable.

I had Weatherby do a project for me with two 16" rifles, a 308 and a 7mm08

When I installed my can on the latter it was NOTICEABLY at an angle.
Needless to say, back in the box it went.

As much as cans cost, plus the tax stamp, not to mention the waiting, the last thing I want to deal with is a bad thread job.
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#5819514 - 07/06/15 11:06 AM Re: Barrel Threading Concentricity Tolerance ???? [Re: dredd]
catslayer Offline
Tracker

Registered: 12/11/12
Posts: 973
Loc: Straight out of Johnson County
Guys at Alamo are good people. If Robert says it, I believe it...

money slowly building up to pay for a rifle from them..


Edited by catslayer (07/06/15 11:06 AM)
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#5820096 - 07/06/15 04:29 PM Re: Barrel Threading Concentricity Tolerance ???? [Re: ccoker]
Cleric Offline
Veteran Tracker

Registered: 03/11/12
Posts: 2759
Originally Posted By: ccoker
I don't trust most gunsmith to do threading work.
I do trust Morgan at Dallas Shooting Supplies.
He's fast, does it right and his prices are VERY reasonable.

I had Weatherby do a project for me with two 16" rifles, a 308 and a 7mm08

When I installed my can on the latter it was NOTICEABLY at an angle.
Needless to say, back in the box it went.

As much as cans cost, plus the tax stamp, not to mention the waiting, the last thing I want to deal with is a bad thread job.



Not sure I understand your point about gunsmiths and not trusting them. I think it depends on the smith. If they do primarily AR assembly than I could understand. But there are many gunsmiths that I would trust to thread a barrel. Any that do bolt action rifles should be able to that.

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