polyurethane for seals

[NickG]

After reading about the limited availability of 25mm seals for the TX , I bought some polyurethane and had a go at making some, not for the TX I grant you , I have made a piston head with an o ring and HW fitment for an idea I have for converting the 97 to 25 mm. Pics below hopefully. It does open up the potential for making walther style seals for the TX

http://i1346.photobucket.com/albums/...ps8b590257.jpg

http://i1346.photobucket.com/albums/...psd5a32f0f.jpg

[vobster]

pm sent

[Snooper601]

A 'soft landing' o-ring seal, good potential there Nick.

Cheers

John

[bigtoe01]

A 'soft landing' o-ring seal, good potential there Nick.

Cheers

John

bit like this one i ran on an 80 for a while a few years back..

https://dl.dropboxusercontent.com/u/920660/IMG_3351.JPG

https://dl.dropboxusercontent.com/u/920660/IMG_3353.JPG

[NickG]

bit like this one i ran on an 80 for a while a few years back..

https://dl.dropboxusercontent.com/u/920660/IMG_3351.JPG

https://dl.dropboxusercontent.com/u/920660/IMG_3353.JPG

Everytime I think of some thing new , you seem to have already done it !, What did the shot cycle feel like, I am experimenting with a new piston for the TX with this head on. But My TX is shooting so well at the moment I don't want to take it down just yet. Might have to buy another one.

[bigtoe01]

Everytime I think of some thing new , you seem to have already done it !, What did the shot cycle feel like, I am experimenting with a new piston for the TX with this head on. But My TX is shooting so well at the moment I don't want to take it down just yet. Might have to buy another one.

It was awesome, however i was using modified maccari seals and the meat was thin to machine into....that said if i could get that same seal made with 8mm more meat up front and drop an O ring groove into it I would be running them in all my guns.

Regards me doing everything....i only publish around 30% now, way to much gets copied for financial gain by others. I don't mind sharing, its just some look to others to line their own pockets.

[nced]

Everytime I think of some thing new , you seem to have already done it !, What did the shot cycle feel like, I am experimenting with a new piston for the TX with this head on. But My TX is shooting so well at the moment I don't want to take it down just yet. Might have to buy another one.

I was being plagued on the field target course by temperature induced poi shifting. This was brought to the front a couple decades ago when my brother and I were sighting in for a FT match during snow flurries in the spring at Harrisonburg, Virginia and the temp rose about 25 degrees F during the match. Both my brother and I had a 1" poi shift at only 20 yards so the hunt was on for a way to minimize the contact of piston seal and lube to the receiver tube. My thinking was that temperature variations of about 30 degrees F affect both the durometer of the "rubber" seals and viscosity of the lube being used.

Long story short......I thought my "discovery" was new so after testing I posted my excited report of how much better my R9 shot! I had quite a few positive replies which was too much for one of the "airgun gods" to tolerate. In a very sarcastic reply I was informed that I was only making a big deal out of "reinventing the wheel" since BSA was using oring sealed pistons decades before. LOL.....I later learned that the high power Theoben Eliminator gas ram gun also used oring piston seals so I figured that oring seals couldn't be THAT bad!

Anyway......perhaps there is little thats new under the sun and I personally think that IMPROVING on existing designs is at least as good as doing something new that still needs to be "time tested"!

[brucegill]

After reading about the limited availability of 25mm seals for the TX , I bought some polyurethane and had a go at making some, not for the TX I grant you , I have made a piston head with an o ring and HW fitment for an idea I have for converting the 97 to 25 mm. Pics below hopefully. It does open up the potential for making walther style seals for the TX

http://i1346.photobucket.com/albums/...ps8b590257.jpg

http://i1346.photobucket.com/albums/...psd5a32f0f.jpg

Nice. What's it like to machine? HSS or carbide? Will be good to hear how you get on.

[greenwayjames]

Nice. What's it like to machine? HSS or carbide? Will be good to hear how you get on.

The best and most accurate method, other than molding, is to grind the material. That is the method I was told was used by the airgunsmith I mentioned in an earlier post.

[brucegill]

The best and most accurate method, other than molding, is to grind the material. That is the method I was told was used by the airgunsmith I mentioned in an earlier post.

Thanks. That would exsplain the vmach seal finish maybe? Doesn't look like a normal tool has been used, more of a sanded finish.

[greenwayjames]

Thanks. That would exsplain the vmach seal finish maybe? Doesn't look like a normal tool has been used, more of a sanded finish.

Yep. He used a made up tool post grinder with shaped stones mounted on the slide of one of his lathes. I remember it particularly well because he had the lathe running backwards

[NickG]

Yep. He used a made up tool post grinder with shaped stones mounted on the slide of one of his lathes. I remember it particularly well because he had the lathe running backwards

What on earth is a tool post grinder ! sounds like a complete bodge to me . If you mean he has tried to turn his lathe into an external grinder, then accuracy will go out the window.

I machined my polyurethane using hss, with an oblique cutting angle , similar to what you would use on brass, or phosphor bronze, works reasonably well , but you are never going to get a moulded finish.
I did not want to start a war with this thread, just wanted to encourage others to have a go with polyurethane. I am interested to sell a few bits here and there, but want them to be my own Ideas, whether they are original or not is questionable, as there isn't much in the engineering world that is original , but if you can take an earlier idea and make it work , surely that's a good thing.

[T 20]

Yep. He used a made up tool post grinder with shaped stones mounted on the slide of one of his lathes. I remember it particularly well because he had the lathe running backwards

Hi James

From JB's May 1991 article it reads as he cuts the Polyurethane with HSS lathe tools but says you have to experiment with the cutting angle by grinding the tool ?



All the best Mick

[nced]

After reading about the limited availability of 25mm seals for the TX , I bought some polyurethane and had a go at making some, not for the TX I grant you , I have made a piston head with an o ring and HW fitment for an idea I have for converting the 97 to 25 mm. Pics below hopefully. It does open up the potential for making walther style seals for the TX http://i1346.photobucket.com/albums/...ps8b590257.jpg http://i1346.photobucket.com/albums/...psd5a32f0f.jpg

I'm a "Yank" so my R9 (rebadged HW95) was tuned to about 14.5 fpe and I found that the polyurethane seals eroded rather quickly at the transfer port area. While the edges of the seal were still pliable, the center of the seal was eroded and hardened like a cinder. It was at that time a couple decades ago that I started messing with aluminum oring sealed piston caps to solve the "erosion issue" and have been using the alloy caps since. Here are a couple pics of eroded HW piston seals from that time..
The samples above weren't polyurethane and MYpoly piston seals eroded MUCH worse. In the beginning I would cut my piston caps with enough clearance between the piston face and seal to fit a thin polyurethane washer as a sort of "shock absorber". After a while I found that when properly balanced there was no need for this bumper since the piston decelerates on the high pressure column of air just before the pellet starts moving through the barrel. When I first started cutting piston caps I pulled apart my R9 after several thousand shots to inspect the oring and this is what I found.......

No impact damage at all on the face of the aluminum piston cap with power levels of 14.5fpe.....just some "combustion coloring" from the molly bearing lube that was used.

I have moderated my R9 power level to about 12.5fpe for the last few years since I believe that the R9/HW95 simply "shoots better" at this power level so I'm wondering if "piston cap burning" would be an issue if the caps were made from molly filled 6/6 nylon (Nylatron) instead of aluminum. When first cutting polyurethane seals and noting the erosion of the seal face I did a little "heat resistance test". I played the flame of a propane torch over a piece of polyurethane and it actually melted rather quickly like a sticky wax. Matter of fact, I would melt the face of a short section of rod and stick it to a steel mandrel for spinning in my lathe for cutting piston seals. Later I did the same "flame test" on a piece of 6/6 nylon and found that it didn't melt, but after more heat than used to melt polyurethane.....the nylon simply charred into a cinder. I did the same test with acetal (Delrin) and the temperature resistance was between that of polyurethane and 6/6 nylon. Since the acetal machines very nicely whereas 6/6 nylon is tougher and harder to machine, perhaps it would be a good "bearing type replacement" for aluminum for an oring sealed piston cap.

[NickG]

I'm a "Yank" so my R9 (rebadged HW95) was tuned to about 14.5 fpe and I found that the polyurethane seals eroded rather quickly at the transfer port area. While the edges of the seal were still pliable, the center of the seal was eroded and hardened like a cinder. It was at that time a couple decades ago that I started messing with aluminum oring sealed piston caps to solve the "erosion issue" and have been using the alloy caps since. Here are a couple pics of eroded HW piston seals from that time..
The samples above weren't polyurethane and MYpoly piston seals eroded MUCH worse. In the beginning I would cut my piston caps with enough clearance between the piston face and seal to fit a thin polyurethane washer as a sort of "shock absorber". After a while I found that when properly balanced there was no need for this bumper since the piston decelerates on the high pressure column of air just before the pellet starts moving through the barrel. When I first started cutting piston caps I pulled apart my R9 after several thousand shots to inspect the oring and this is what I found.......

No impact damage at all on the face of the aluminum piston cap with power levels of 14.5fpe.....just some "combustion coloring" from the molly bearing lube that was used.

I have moderated my R9 power level to about 12.5fpe for the last few years since I believe that the R9/HW95 simply "shoots better" at this power level so I'm wondering if "piston cap burning" would be an issue if the caps were made from molly filled 6/6 nylon (Nylatron) instead of aluminum. When first cutting polyurethane seals and noting the erosion of the seal face I did a little "heat resistance test". I played the flame of a propane torch over a piece of polyurethane and it actually melted rather quickly like a sticky wax. Matter of fact, I would melt the face of a short section of rod and stick it to a steel mandrel for spinning in my lathe for cutting piston seals. Later I did the same "flame test" on a piece of 6/6 nylon and found that it didn't melt, but after more heat than used to melt polyurethane.....the nylon simply charred into a cinder. I did the same test with acetal (Delrin) and the temperature resistance was between that of polyurethane and 6/6 nylon. Since the acetal machines very nicely whereas 6/6 nylon is tougher and harder to machine, perhaps it would be a good "bearing type replacement" for aluminum for an oring sealed piston cap.

Very interesting post, I have been using delrin o ring heads on my pistons, to good effect, there is no discernible wear after thousands of shots, The poly is an attempt to improve the already tame firing cycle, maybe I am already there.