Canadian Airgun Forum

The #1 Community for Airguns in Canada!
It is currently Fri Nov 22, 2019 5:32 pm

All times are UTC - 5 hours


The Canadian Airgun Forums are a place for people to discuss and learn about airguns and the airgunning sport in Canada. There are lots of discussions about airguns, airgun accessories, reviews, modification and repair information, airgun events, field target and free classifieds!

 

You need to register before you can post: click the register link to proceed. Before you register, please read the forum rules. By joining our free community you will have access to post topics, communicate privately with other members (PM), respond to polls, upload your own pictures, and access many other special features. Registration is fast, simple, and absolutely free! To start viewing messages, select the forum that you want to visit from the selection below.








Post new topic Reply to topic  [ 4 posts ] 
Author Message
PostPosted: Fri Oct 14, 2016 5:58 pm 
Offline
User avatar

Joined: Sat Nov 03, 2007 4:19 pm
Posts: 8979
Location: Coalmont BC
Quite a long time ago I made some alignment tools (pilots) out of wood to allow me to set the stripper cone parallel to the bore on installations where the alignment wasn't great, and I had drilled out the outer stripper housing and installed six setscrews to allow me to move the cone around....

Image

While these did a great job of what they were intended for, adjustment of the gap was primarily an eyeball thing.... A few months ago, when I changed over my Hatsan AT-44 S-10 Long to shooting the 34 gr. JSB Heavies, I checked the alignment of the stock Hatsan Stripper with one of my pilots, and found it was virtually perfect.... At the time, I had been reading up on Barrel Harmonic Tuners, and several people told me that just a few thou change in the position of the adjusting weight can drastically affect group size.... Simultaneously, I read a few articles about Air Strippers, and the opinion is split about which is the operative factor, the gap between the muzzle and the stripper cone, or the effect of moving the weight of the cone back and forth.... I think it may be a combination of the two, but in reality DOES IT REALLY MATTER?.... I mean surely the goal is to reduce the group size as much as possible by moving the cone back and forth until you find the sweet spot where the group is the smallest.... So, I decided to design an adjustable version of the wooden pilot above, that would allow me to change the position the cone by just a few thou at a time, and would also be repeatable.... I came up with the following design, but it had to wait until the Motel wasn't so busy and I had some time to get into the shop to make it....

Instead of all wood, the core of the new pilot is turned from a 1/2" steel rod.... The mid-body is a precise slide fit in the stripper cone, which will vary with caliber.... There is a shoulder above that which is just under 12mm (the OD of the brass cone) so that it can push the cone into the hole in the stripper body when required.... Behind the mid-body the steel shaft is turned down to 3/16", and a piece of hardwood dowel, drilled out to 3/16", is pressed onto it.... The OD of the dowel is then turned down until it just slides into the muzzle.... The center hole in the end of the steel shaft insures it remains concentric with the midbody of the pilot that slides into the cone while turning the OD of the wooden bushing.... This insures the cone and bore are concentric and parallel....

Image

The aluminum "nut" and the front of the steel shaft are threaded 1/4"-28, so that each turn is 0.036" of travel.... That works out so that 10 deg. of rotation is 0.001".... There is an 8-32 setscrew pushing lightly on a short piece of 1/8" Delrin rod against the threaded shaft to act as a brake to keep it from self-adjusting, and a screw slot in the end of the shaft for adjustment.... Turning the shaft changes the position of the shoulder on the shaft relative to the end of the aluminum collar, which in turn pushes the cone deeper into the body of the stripper when the aluminum collar is pushed against the end of the stripper body.... In the photo below, the cone is at the deepest position, with about a 1/2 caliber gap between the muzzle and the end of the cone....

Image

In the photo below, the cone is slid out far as it can go, and the gap is about 2.5 calibers.... The cone has a slot which limits it's travel before it hits the setscrew in the stripper body.... There is a 1/2" diameter milled pocket that is 0.4" deep in the aluminum collar to allow the shoulder on the pilot a place to go when the collar is screwed in to retract the cone position.... The gap you see between the collar and the stripper body is the total adjustment range, which is 1/2"...

Image

With the collar threaded down until the cone has the largest possible gap, it looks like the photo below.... You can see the shoulder on the pilot up inside the aluminum collar, and the center hole in the end of the steel pilot shaft with the wood bushing to protect the bore.... If you look closely, you can see a center punch mark at the end of the screwdriver slot, so I can tell full turns from half turns, and of course I can also measure how far the threaded shaft sticks out of the aluminum.... This is not a difficult tool to make on a lathe, but it is surprising how much time even a simple project can eat up.... about 4 hours in this case, plus the design time.... and then the time to write up this report of course....

Image

I hope the photos and the description make it clear how it was made, and how it works.... My plan is to start like this, with the cone fully out, with the screw slot and center punch mark pointing at the set screw hole in the collar.... I will slide it in until the collar touches the end of the stripper body, snug the setscrew holding the cone in place, slide out the tool and shoot a group at 50 yards.... I will measure and record the group size, screw the threaded rod in one turn, slide the tool back into place, loosen the setscrew until the cone moves in 0.036", snug it up and shoot another group.... I will keep doing this until the cone is as far in as possible.... That will take 14 turns, so the initial test will be 15 targets.... Graphing the results should quickly narrow down the best position of the cone, and at that point I plan to repeat the process with 1/4 turn adjustments, or less if required.... If there are two (or more) sweet spots, I can explore them both, possibly at different ranges.... I think you could spend a whole day (or a few days) just tuning with this device.... I hope it's worth it.... :roll:

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


Top
 Profile  
 
PostPosted: Fri Oct 14, 2016 7:33 pm 
Offline
User avatar

Joined: Sun Jul 01, 2012 4:25 pm
Posts: 199
Location: HRM N.S.
I look forward to seeing the results of your tests, always enjoy following your posts.
I don't currently have or use an Air Stripper but I do find them interesting.
Cheers

_________________
"Quando omni flunkus moritati"


Top
 Profile  
 
PostPosted: Sat Oct 15, 2016 8:36 pm 
Offline

Joined: Mon Sep 17, 2007 8:13 am
Posts: 1063
Location: Victoria, B.C.
I'd buy one or even one of your examples if these help with grouping things as I also have an air stripper. My grouping is good but maybe I could get them tighter with your jig-a-ma-jig.


Top
 Profile  
 
PostPosted: Sun Oct 16, 2016 5:07 am 
Offline
User avatar

Joined: Sun Jan 09, 2011 8:07 am
Posts: 3320
Location: Central West River Nova Scotia
Very interesting Bob. When you find that sweet spot for the cone, What about adjusting the depth of the whole stripper on the muzzle ? Instead of threading it all the way tight, back it out a half turn or so, then shoot, then back it out again and shoot, etc... Also changing the position of the three vents. For instance, if two of the three vents are facing down with one pointing straight up, is there a difference with two vents facing up and one facing straight down, or perhaps no vents facing straight up or down, but somewhere in between ? The air jet from the vents, and the direction they exit, might also play a role in the harmonics.

_________________
If I had only one wish, it would be to be able to "unsay" things.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 4 posts ] 

All times are UTC - 5 hours


Who is online

Users browsing this forum: Majestic-12 [Bot] and 0 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
News News Site map Site map SitemapIndex SitemapIndex RSS Feed RSS Feed Channel list Channel list

Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group

phpBB SEO