Canadian Airgun Forum

The #1 Community for Airguns in Canada!
It is currently Sun Nov 17, 2019 7:47 am

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  [ 9 posts ] 
Author Message
PostPosted: Mon Aug 29, 2016 2:27 pm 
Offline

Joined: Tue Oct 18, 2011 12:21 pm
Posts: 431
Location: Ontario
Fiddle long enough with an object and eventually something will get broken.

In the process of diagnosing what is causing the problem with my Crosman 451 homemade hammer, I did a computer model. Also, to confirm that my model looks right, I was observing the movement of the secondary sear through the space visible when the side grip panel is removed.

Being in an awkward position to, at the same time, cock the hammer and look at the secondary sear, it finally happened. I dropped the pistol on the floor.

It didn't fall from very high (I was sitting) and not even on a hard surface (there is a carpet on the floor) but a corner of the rear sight shattered rendering it unusable.

This happened yesterday and tomorrow I am going back to work. So this is it, it needs to be fixed today.

Just to see if I couldn't find a rear sight assembly or a blade on the internet, I did an internet search. I was not too hopeful as there are not a lot of spare parts floating around for the Crosman 451.

Surprisinly, I got a hit... but it was already sold.

Suddenly I looked at the picture more carefully!

Wait a minute!!!

This blade has a broken corner just like mine.

Image

After reading the description in the ad, the seller was saying that he found a good rear sight replacement and he was selling his broken one.

So it seems that I am not the only one to whom that happened. I think that the rear sight blade is also a sintered steel part. It would be very complicated to machine because the thread for the sight adjustment is only in one half of the plate thickness. Trying to redo one, in a conventional way, would necessitate to start with a plate at least 3 times the final thickness, drill and tap in the middle and machine down one face to the centerline of the tread and on the opposite face, reduce the thickness but leave some meat where the cylinder of the threaded hole is. This is probably why Crosman used sintered steel and also why it broke when it fell on the carpeted floor.

Nothing is simple. To lock the adjustment screw so it won't come apart, no loctite was used but instead there was pin prick blow that deformed the end of the screw and the face of the nut. Now try to take it apart. No fun.

I finally had to drill a little bit to clean the interference and I was able to disassemble the rear sight.

Unfortunately, the part list diagram shows the rear sight as a single component: Rear Sight Assembly.

This means I should also have paid more attention to previous photo (the one from the internet) before starting to remove the adjustment screw (that is after I was able to unlock it from the nut).

After a few turns, what do you think happened?

Yes, I practically got hit in the eye by a small detent ball. I heard it fell on the floor and never was able to found it back. It could have been avoided it I had looked at the previous photo before starting. It is visible on the upper right side close to the sight body.

The following picture is my mine. It could be recognized by the absence of the small detent ball. (Later at reassembly, I also discovered that there was a small washer still in the cavity for the nut. It doesn't appear in the picture but if you disassemble you rear sight just remember that it is there so you won't lose it).

Image

As mentioned, making an adjustable blade would be too complicated to make at home so I opted to transform the rear sight into a fixed sight.

I had a small piece of .015" brass shim stock. Once folded in half and a sharp crease made for the top edge it was about 1/32" thick. This would be too thin to fill the space. Because the stuff has a natural springiness there is a gap at the bottom and this would be about right space to get the screw going in the middle.

Image

I used the sheet metal snipper to cut the shape of the blade so the vertical portion of the "T" is the size of the slot width and the top is the same width as the sight body. A small file was used to clean the edges and cut the notch.

Then the metal was formed to wrap around the screw (a bit as what can be seen on the broken original). The final touch was to blacken it with a Sharpie.

Image

For future use, I put aside the broken blade, the detent spring and the small piece of sheet metal that acts as a spring spacer. This spring spacer is to keep the thread of the blade in contact with the thread of the adjustment screw.

For my fixed rear sight assembly, I just kept the main body, the adjustment screw, the nut and my replacement home made sight blade.

This is how it looks on the pistol.

Image

I did some tests and it shoot centered, I just needed to reset the elevation and it was done.

R-Gun Pete


Top
 Profile  
 
PostPosted: Mon Aug 29, 2016 4:18 pm 
Offline
Supporting Member 2009
User avatar

Joined: Tue Aug 21, 2007 5:25 pm
Posts: 615
Location: Burl, Ont.
That sight blade looks similar to a 38C or T early blade...


Top
 Profile  
 
PostPosted: Mon Aug 29, 2016 9:16 pm 
Offline

Joined: Tue Oct 18, 2011 12:21 pm
Posts: 431
Location: Ontario
Thanks rick'o'shea!

One of my 38T has a plastic rear sight (variant 2) but the other has the rear sight with the metal blade (variant 1).

You are right, it looks very similar to the blade on the 451.

I will try to buy one, maybe 38 parts are still available.

Otherwise, I will also try to see if the one that is broken could be silver soldered.

If it works I could put the repaired blade on the 38 and swap the good one to the 451.

That was a good suggestion.

R-Gun Pete


Top
 Profile  
 
PostPosted: Mon Aug 29, 2016 9:35 pm 
Offline

Joined: Wed Feb 04, 2015 7:23 pm
Posts: 140
Location: Canadian Prairies
It sure does look like the old style 38 sight blade. Have seen several broken exactly like that. It doesn't take much.
Crazy glue the broken piece on in a pinch. Silver solder even better.

The 451 part diagram posted in an earlier thread shows several part numbers from the 38: such as the elevation screw, and the parts from around the cartridge end seal (old style 38-96), piercing pin (old style38-27) and screen (38-28).

I bet the 38-7 sight blade and 600-6 detent ball will fit the 451.

JG Airguns has the 38-7 sight blade. $7.00 US and 600-6 rear sight ball $2.35 plus shipping etc.

Full 451 sight with pivot link assembly $75. Ouch!

R-Gun Pete: if you contact John G at JG, he should be able to tell you if the parts are a match. http://jgairguns.biz/catalog/contact_us.php

Or maybe just CAD one up and 3D print the blade! :idea:

Cheers!


Top
 Profile  
 
PostPosted: Tue Aug 30, 2016 8:02 pm 
Offline

Joined: Tue Oct 18, 2011 12:21 pm
Posts: 431
Location: Ontario
Hi ColdAir!

Thanks for the informations, I will keep the links for referral.

As it is, I would prefer not to spend more money if I don't need to.

My Crosman 38T is not collectible anymore because the paint was bad when I got it and decided to glass bead it.

Image

So it wouldn't be a big deal if I scavenge the metal bade from it to install it on the 451.

I could put back, on the 38 , the soldered blade if I can do the repair or, as you suggested, make a plastic part from the 3D printer.

R-Gun Pete


Top
 Profile  
 
PostPosted: Thu Sep 01, 2016 9:40 pm 
Offline

Joined: Wed Feb 04, 2015 7:23 pm
Posts: 140
Location: Canadian Prairies
R-Gun Pete,

If you did design and 3D print the sight blades I bet you could find quite a few 'customers'. I would likely buy a handful.

Nice grips on that 38T by the way.

Cheers!


Top
 Profile  
 
PostPosted: Sun Sep 04, 2016 10:35 am 
Offline

Joined: Tue Oct 18, 2011 12:21 pm
Posts: 431
Location: Ontario
Hi ColdAir!

Sorry for the delay in answering your question. Busy week back at work.

First, just to clarify the idea of 3D printers that people have.

They are not intended as production tools. They are excellent to get prototype at a very good price but for regular mass production they are not cost efficient.

Each system has it own quirk but basically it is all the same. There are two types of material, one for the model and one for the support. Most of the time the model is embedded in support material which has to be removed and this could be time consuming.

Material, machine time and manual labor required to get the final part ready to be used needs to be computed in the final cost( and all that adds up).

Furthermore CAD model are not too good to make actual thread and for the sight that would be critical because it is part of the adjustment.

Image

This is probably the reason why Crosman used sintered steel for those sight for the 451.

The powder is pressed in a mold and no other machining is required which keeps cost down.

In short the answer is I would not be able to get involved in production of parts to sell.

R-Gun Pete


Top
 Profile  
 
PostPosted: Sun Sep 04, 2016 10:55 am 
Offline
User avatar

Joined: Wed Jun 06, 2012 5:06 pm
Posts: 111
Location: Ontario
Or you could just get a two part clear epoxy from the dollar store, not C.T expensive and same stuff. Sometimes its better to do things in a more simpler manner. IMO :wink:


Top
 Profile  
 
PostPosted: Sun Sep 04, 2016 3:38 pm 
Offline

Joined: Tue Oct 18, 2011 12:21 pm
Posts: 431
Location: Ontario
Hi niblixdark!

I didn't have time yet to check with my friend about brazing or silver soldering.

If it doesn't work, I will keep in mind your suggestion for the epoxy.

I am not sure if on top of the repair on the broken surfaces maybe it would need to have a thin coat applied over the whole sight (except for the bottom of the "T" which must stay the same thickness to fit in the slot).

It might be necessary to reinforce it because that rear sight assembly takes a beating everytime the pistol blowback.

Thanks.

R-Gun Pete


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 9 posts ] 

All times are UTC - 5 hours


Who is online

Users browsing this forum: No registered users and 1 guest


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