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Centering a Barrel Using Interapid 0.0001" DTI with 2.75" Point - Cont. w/ Second Vid

hepburnman

Aluminum
Joined
Feb 20, 2013
Location
NJ
Centering a Barrel Using Interapid 0.0001" DTI with 2.75" Point - Cont. w/ Second Vid

Here is the second video where the Interapid DTI's point has been retracted 1" (from the 2.5" spot in the bore) and this would be about where the base of my bullet would be in the case. I've adjusted the spider only here to achieve the centering you see and I've tuned for about zero indicator movement in the grooves/tops of lands.

I am intending to use the Interapid DTI with the 2.75" point, when I finally do cut the chamber this barrel, because even the Mitutoyo 513-504 DTI cannot reach 2.5" into the bore even if I pre-drilled and bored. Once it is centered with the Interapid DTI, and is then pre-drilled and taper-bored, I will switch to the Mitutoyo DTI and at least re-indicate the rear-portion of the throat area that I will be able to reach. My sensitivity now will be 0.0001" rather than ~0.0004" that I had with the Interapid DTI with the 2.75" point. If center-adjustment is found to be needed with the Mitutoyo DTI I will re-bore the barrel as needed before reaming.

 
I am a hobbyest gunsmith and I am using the range rods to center de barrel for chamber work. I pré drill, insert the range rods, indicate ,bore and then use the reamer. Using this method, the measuring point is the lands. If you use the DTI indicator, what is your measuring point, as the lands and grooves may have not the same dimensions one from another?
Just need understand new ways, as I need learn a lot.

Excuse my bad english too

Thanks
 
I am a hobbyest gunsmith and I am using the range rods to center de barrel for chamber work. I pré drill, insert the range rods, indicate ,bore and then use the reamer. Using this method, the measuring point is the lands. If you use the DTI indicator, what is your measuring point, as the lands and grooves may have not the same dimensions one from another?
Just need understand new ways, as I need learn a lot.

Excuse my bad english too

Thanks

Hi- I work with bad english! :) You will get many different recommendations for which is the better method to use (please no flames!) but I have chosen to measure/indicate the grooves and lands directly rather than use a range rod, or other type rod, that locates only on the tops of the lands and that must also have some clearance (error-comtributers) between the components to slip into the bore, etc. By using a DTI with a long enough point, to reach up into the critical throat-area of the bore (I am assuming that we agree that alignment of the bullet to the bore immediately in front of it is most critical), both the groove diameter/circle and also the tops of the lands/circle can be measured directly without the possibility or errors due to clearances between components. You also have the advantage that you can decide which is best to align to your spindle's center; groove or land circle. You can also see here too if the two are reasonable concentric to one another in this critical area.

Once the barrel is aligned concentric to the lathe's spindle, by the DTI with the long-point method, the chamber area can then be pre-drilled and bored, prior to reaming, and then when you ream you would be certain now that the chamber will also be well aligned with the bullet/throat area (please no flames here too as I will say that this is just my oppinion and no indifference meant to your method). :)
 
Thanks Hepburn.

But you indicate in the spindle area centering in the jaws with cooper wire and in the opposite side with bolts?

Not sure about the correct words...:confused:
 
Thanks Hepburn.

But you indicate in the spindle area centering in the jaws with cooper wire and in the opposite side with bolts?

Not sure about the correct words...:confused:

In initially setting up the barrel and indicating it for concentricity with the lathe's spindle this was performed prior to the video in my first posting with this same title. Here, I used close fitting reamer bushings pushed most of the way into the bore at both ends of the barrel and, while indicating on these bushings, I then adjusted the 4-jaw chuck and also the Spider at the muzzle-end by adjusting the 4 screws there. Once I got the barrel centered real close I switched to the Interapids DTI and inserted its 2.5" point into the bore and then adjusted only the jaws of the chuck to get this forward throat-area to run concentric. I had a ring of heavy copper wire wrapped around the barrel at this 2.5" location as well. This formed a pivot point for the barrel at this point so when I retracted the DTI point by 1" to indicate this area of the throat, and then adjusted only the screws of the spider, the concentricity of the bore right at the 2.5" location did not change. My purpose was to get a 1" long cylindrical area of the bore, where my bullet resides, to run as concentric with the spindle as possible. With this area running true I can then pre-drill and bore the reminder portion of the barrel and when reamed this area too will be concentric with the 1" cylindrical throat-area.
 
Thanks hepburnman.

I searched but not sure what Interapid model to choose. (you know, my english...)
Would you please post a link to the exact model to purchase?


Thanks
 
Thanks hepburnman.

I searched but not sure what Interapid model to choose. (you know, my english...)
Would you please post a link to the exact model to purchase?


Thanks

Not Hep, but I can answer.

312B-15 is a .0005 with a 2.75 inch tip. It will reach in far enough to indicate most throat areas.

Another way to do it is to buy a

312B-3 which is a .0001 indicator with a .687 inch tip. You can get the 2.75 tip and install it. Switching tips is common with indicators, but it must be remembered to take into account the desensing the longer tip will cause. With the 2.75 inch tip, the 312B-3 will become a .0004 per division indicator.

Both the numbers I quoted have the 1.5 inch dials. I have one with the 1 inch dial which I seldom use.

If there is a V behind the part number, it is a vertical indicator which would be more difficult to use for the intended work.

Please note: If buying on eBay (or the like) 310 indicators are at least 30 or more years old. There are no more parts available for them. When broken they are trash, they really can't be fixed.

I have seen stuff on eBay with all kinds of tips that are not Interapid, do not assume anything has the correct tip. There are 3 tip sizes for Interapids (English), .687, 2.75, and 5.5 -- Only two metric sizes, 15.2mm and 16.5mm. There are many ball sizes and materials. There are a few converters for tip shanks, but truthfully, each indicator model is made for a certain tip and is only accurate with that tip.

Just some info,
Art
 
What is the repeatability spec on the .0001" indicator? What is that spec once you add a 2.75" tip? Is there one?
What is the repeatability spec on the .0005" indicator that is calibrated for the factory installed 2.75" tip?
 
There may not actually be a repeatability spec for the 0.0001" indicator with the 2.75" point as this indicator may not have been designed to use this long of a point.

I can only say that Long Island Indicators said there might be issues using it with the long point, but I dont beleive I have seen any of these, and also, my "repeatability" seemed to be fine when I did my centering of the barrel - the needle looked like it was repeating to the same point where it should have. I used the DTI with the point down but preloaded against the bottom of the bore. This supported the extra weight of the point, compared to the .63" one, and also it looked like the DTI was reacting pretty fast to the changes in readings going from the tops of the lands to the grooves and back again. Maybe not a great use-application for their DTI but in my case, and the way I used it, it seemed to work OK.

There most likely is a repeatability spec for the 0.0005" DTI but I'd have to look for it. Maybe The LI Indicators site may have it?
 
What is the repeatability spec on the .0001" indicator? What is that spec once you add a 2.75" tip? Is there one?
What is the repeatability spec on the .0005" indicator that is calibrated for the factory installed 2.75" tip?

.00005 on the .0001 indicator. No specs on the .0001 with the 2.75 tip. Since it is essentially a .0004 indicator, .0002 repeatability would be a good guess.

The repeatability spec on the .0005" indicator that is calibrated for the factory installed 2.75" tip is .0002, that is a stock indicator number 312B-15 (74 111965).

This is all dependent on the tip being at a 12 degree angle to the measuring surface. Otherwise, cosine error must be factored in. This is important and significant when cramming an indicator with a long tip up a barrel's butt.

Art
 
Right now we need to NOT get too far from the objective. As it stands, the work here could be done with a Starrett indicator, which was probably the worst name brand indicator ever made. That being said, we have Interapids. Here we will be using the indicator as an indicator, it's intended purpose. For centering, preload is essential. Preload to beyond the max expected deviation if possible. The specs of the indicator are not tremendously important, getting an indication (deviation from square or round) is most important.

I don't like to use an indicator to measure, but to indicate.

Art
 
Interapid

.00005 on the .0001 indicator. No specs on the .0001 with the 2.75 tip. Since it is essentially a .0004 indicator, .0002 repeatability would be a good guess.

The repeatability spec on the .0005" indicator that is calibrated for the factory installed 2.75" tip is .0002, that is a stock indicator number 312B-15 (74 111965).

This is all dependent on the tip being at a 12 degree angle to the measuring surface. Otherwise, cosine error must be factored in. This is important and significant when cramming an indicator with a long tip up a barrel's butt.

Art

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I just bring this Interapid from USA. Cost me a lot of money,with customs charge.

As I never handled this device, I have a question. I can change the tip position, to reach deeper in the barrel?

Interapid.jpg
 








 
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