Nylon screw piston buttons

[TooJung2Die]

I have had no luck with piston buttons that are held on with Super Glue. The glue doesn't want to stick to the kind of plastics I tried. I don't have the tools to make a flat bottom depression for the button. Then I had an Idea... I used a B3-3 air rifle as the test bed so if the idea didn't work I could remove the buttons and no great loss.

I used Nylon M6x1.0 screws because I have a tap in that size and a supply of those screws. There is an unthreaded shoulder under the head of the screw. The shoulder will be the button.

I drilled three #8 holes in the skirt of the piston evenly spaced with one hole opposite the cocking slot. I tapped the holes with a M6x1.0 tap.

I put a Nylon screw in each hole, tightening them up against the shoulder. At the last minute I decided to put Super Glue on the threads of the screw for more secure hold.

I cut off the excess threads inside the piston and used a Dremel sanding drum to sand the screws flush. Again using the Dremel sanding drum I removed the screw heads leaving the shoulder sticking above the piston skirt.

The last step was hand sanding the buttons until the piston fit. I ended up with .010" of the buttons above the surface of the piston skirt.

The piston is a very tight fit going into the compression tube by the trigger but slides nice and free in the area it normally operates. I have inserted and removed the piston a few times and the buttons stayed firmly in place despite the high friction during install and removal. When the buttons wear out the old ones can be removed and new buttons installed.

Cocking and firing the gun is smoother and quieter than before. I still have to run some pellets over the chrony to see if it made a difference in velocity. If these buttons hold up well I'm going to install them in a Crosman Fury next.

Here are some photos I took during the making of the buttons:

[Roadworthy]

Jon, I'm really glad it worked out for you.  The screws won't come out on their own.  The cylinder will hold them in, they have nowhere to go.

The Fury may be a problem.  I have a Nitro Venom and the piston is HARD!!  I gave up and put three dots of "Liquid Steel" on the skirt, then filed it to the correct height.  The skirt of the piston has a 45 degree bevel, resulting in a sharp edge.  I rounded the edge on a bench grinder and then lubed it well.  Now we're at "wait and see".

If you want depressions in your Fury piston and find it's really hard, you can do rounded depressions with a Dremel stone.  If you want flat bottom depressions try an end mill.  You can then put epoxy in the depressions and sand or file to height.  There is no way I would try to tap the skirt.  If the tap breaks you've got serious trouble.

[HYspd]

don't bother trying to glue nylon, it doesn't have any of the electrical, chemical or surface properties required for an adhesion process to happen ...

you might be able to encase a nylon part with glue that is stuck to another material, but it's the glues own shape holding ability that is providing the retention effect not the glue sticking to the nylon..

instead leave thread or two on the inside of the piston and melt it down with the back of a moderately hot spoon to smear the melted nylon around a bit to make it larger than the thread diameter..that will create a locking effect if the screws ever try to back out

you can do the same on the head end to shape and enlarge the contact patches...


for drilling through hardened metals you can use cement drill bits..they have carbide inserts on the cutting edges..make sure to check the cutting edge...you want the one that looks like a crude version of a regular drill...in stead of all the angles and curves, there is the flat face of the carbide insert and the bottom end (goes towards the metal when drilling) of the insert is flat and angled (relieved, this is the "relief" angle) so that the drill can cork screw into the metal as the drill is turned...

if the bottom of the insert has a very wide open V shaped like a badly sharpened chisel point, then that is the WRONG type.....the chisel points are just exactly that... chisels... that type is for use with a hammer drill when driving a drill into hard rock....

it will take a lot pressure like a dull regular drill and you can motor oil for a cutting lubricant if you don't have any real machining oil on hand....but don't use anything else for lube...motor oil at least has some extreme pressure resistance that few if any other oils will have that aren't made for cutting metal...

a 3/16" drill will work with a 6mm tap...even if the material is hard it will leave enough of a thread to guide a 6mm screw into place...if you do the melt thing it will stay put.....i think you can get solid nylon rod at some hobby shops...melt a head on to it and cut it off the rod then melt it on the back side to set it...

I think delrin responds to the melting trick too but's been a long time since I tried heat fitting delrin..

[avator]

I poated in another thread, My nitro venom was grinding real bad, gouged the inside of the cylinder. I don't have the fancy machine shop tools either so buffed the gouged area as best I could. ThenI cleaned the piston skirt, then cleaned it with alcohol. I super glued 4 nibs of soda bottle (1 on each side of the gouge and 2 opposite). About 200 shots so far and it's still smooth as butter. But, they could come loose tomorrow, who knows. And if and when they do, I'll buy a cylinder. I figured it can't hurt to try, this cylinder is already hosed.

[TooJung2Die]

I "ghetto tuned" the piston with a soda bottle sleeve inside the piston while the gun was apart for the buttons. The sleeve worked very well as far as reducing noise from the main spring. I shot it several hundred times. Trouble is, the velocity dropped by about 25 fps so I took it apart and removed the sleeve.

These nylon buttons are tough. Nylon is used for bushings and bearings. The most wear will be on the button opposite the cocking slot. They didn't loosen and showed no visible sign of wear. The height measured exactly the same. When making a glue or solder connection it is important to first make a good mechanical connection. The threads in the holes and tightening the screws down against the shoulder accomplishes that. Even though Super Glue doesn't bond to Nylon having it in the threads fills any minute gaps and adds strength. The shoulder will keep the button from getting pushed through the threaded hole. The cylinder walls will keep them from coming out.

After reassembling the gun without the sleeve I got the velocity and spring twang back. Shot it several hundred more times. I need to find a bottle with thinner plastic. The 3 liter bottle I used was .015" thick.

Is that B3 piston fugly or what?   So far, so good as far as the button experiment goes.   

[TooJung2Die]

I found a water bottle with .010" walls. I took out the piston and inspected the nylon buttons. Still holding up great, no wear, still .010" high all around. The new sleeve is in place and the shot cycle is smooth and quiet. I'm keeping the sleeve in the piston even if it does reduce velocity a bit. The benefits outweigh the slight drop in velocity. Back to the chrony to see what the results are.

I believe you when you say the piston skirt is hard. Of course I'll have to see for myself. 

[nced]

For buttoning piston skirts I used to first anneal the hardened skirts with a propane torch and then use a HSS 1/4" endmill to cut the pockets using a drill press and a solidly clamped piston. Then I tried a solid carbide 1/4" endmill and found that it would cut a pocket in a hardened R9 piston skirt without annealing. The 1/4" diameter solid carbide endmill costs less than $10 from this source............
http://www.lakeshorecarbide.com/4fluteuncoated-2.aspx
Works well with a bit of cutting oil but there is the need to solidly clamp the piston in place. Here is a pic of a piston that was buttoned with 1/4" diameter molly filled 6/6 nylon buttons.........

The pockets are about .015 deep, the buttons are secured with "SuperGlue", and then trimmed to fit the receiver by spinning in my lathe chuck. I figure that if the glue was to let loose it would happen as the buttons were pounded on the lathe bit as they were trimmed. Once trimmed to fit there is no issue with a loose button once installed, even if the glue let loose, because the buttons are trapped between the bottom of the pocket and the receiver ID.

I've been running an oring sealed piston cap on my R9 piston and the piston was both buttoned plus machined to reduce the weight. This arrangement has worked well for a couple years but I recently ordered a new HW95 piston to play with. I recently tuned a HW97 for a fellow and noticed that HW has changed the design of their piston seals like this...........

The new style HW piston seal had a rather wide "parachute" as opposed to the older "thin parachute" plus the new style has a reduced diameter base. The intent is to test the new piston seal against my home rolled oring sealed piston caps since the "sealing surface" of the new seal seems similar to the "sealing surface" of my orings.

Anywhoo........noticing that my newest R9 (a couple years old now) had a very nice piston to receiver fit needing only a couple thou projection of buttons I think I'll depart from even buttoning the new piston. When the new piston arrives (I expect it this week) I'll be using the new style piston seal on an unaltered piston, EXCEPT I plan to actually polish the outer surface of the piston. I'm guessing that the polished hardened surface of the piston skirt lubed with Krytox will work just fine without buttoning. Hummm....I guess that IF the "unaltered but polished piston" or the new style piston seal has issues I'll simply button the skirt and mount another oring sealed piston cap.  

[TooJung2Die]

HYspd says don't bother trying to glue nylon and nced says he attaches moly impregnated nylon buttons with superglue. A lot of discoveries were made because someone didn't know it couldn't be done and went ahead and did it. The drilled and tapped nylon screw buttons will probably stay put without any glue. I used superglue for added insurance.

I have some thin Teflon washers, about .75" diameter. I cut some buttons out of that and used superglue to attach them. I held them in place with masking tape and let them cure overnight. They looked good but peeled off as soon as I hit them with the sandpaper. I thought about using plastic from a soda bottle but thought it should be a tougher material.

At those prices it might be worth it to get an end mill to make button attachment points. Don't know why but it didn't occur to me you can use one in a drill press.
I'm going to do a few more of these nylon screw buttons. I don't have to buy any additonal tools.

I like Krytox and use GPL 106 to lube piston seals. Wonderful stuff, it will not ignite. Ever.