12 replies to this topic

[rork]

One of the most annoying features of the SNAP is the fact that it historically uses a steel pin to retain a comparatively soft plastic catchface; when the pin is pulled across the catchface under the pressure of the spring, it scrapes bits of the catchface away, and eventually, the abraded catch has to be replaced. The bad news is that you're essentially damaging your gun each time you fire it, until it (theoretically) stops working. The good news is that this is really not that big a deal; it's a matter of 10 minutes and 50 cents to replace the catchface, and it only needs to be done about once a season. The great news? Read on.

Materials:

1 1/2" cpvc endcap
2 11/4" OD steel fender washers
1 appropriately sized nylon spacer (look at the photo)
1 #6 11/4" bolt
1 11/4" rubber fender washer
1 11/2" rubber fender washer
1 finishing washer
1 #6 wing nut
Good CA glue
Epoxy putty

Start by gluing the nylon spacer to one of your fender washers.


Now add the second fender washer. Make sure they're nice and centered.

Drill a 1/8" hole in your endcap, and add your bolt as shown.

Glue the washer assembly to the endcap. Make sure it's straight.

Now layer the rest of the components on top, finishing with the wingnut. All pretty standard.

Add a ramp of epoxy putty around the washer. Be conservative in your application; too much will just hamper the priming action of your gun. There should be just enough to "bump" the pin up just long enough so that it slips perfectly into the slot between the steel washers.

You are done. This head should be MUCH more durable than anything that uses a pvc catchface. It is also light and compact, with an amazing seal.
Compared to my old style plunger head:

[Zorns Lemma]

I recall that adding yet another washer to the front (in front of the rubber washer) increases seal under pressure.

Plug the barrel and fire, both with and without another washer to force the rubber to retain against the wall. I'm pretty sure with the front washer "stoppage" time of the plunger rod increase. (I tested in a BBB, maybe SNAP works differently).

Also, I've always been wary of snaps due to how they catch, but this design seems solid enough that I might build one, or a variant on one.

[rork]

The rubber washer fits so tightly in 1 1/4" pvc that I don't think it would fit with another steel washer in front, at least without binding and deforming and/or tearing. I'll probably give it a try next time I build a SNAP, just because I can. As it is, the seal is VERY good.

I'm glad to have caught your interest. It really is a solid concept; the problem arises from the fact that most people's renditions suck.

[venom213]

This is exactly what I have been looking for as of late. I've been frustrated too many times by the usual snap plunger head set up. This is far improved. I now have motivation to work on Snaps, many thanks. I'm thinking about looking around for a rubber peice that would work in place of the epoxy putty. It seems like something that wouldn't be too hard to find

Edited by venom213, 05 December 2009 - 01:19 AM.

[rork]

Rubber's no good. You need something hard and moldable. Epoxy putty fits the bill nicely.

Glad to have inspired your efforts

Edited by rork, 05 December 2009 - 01:31 AM.

[Carbon]

Very nice. The epoxy putty is a good way to create the transition between plunger rod and catchface, without having to do a lot of annoying shaping of PVC.

Ny observations:
There is an issue I see with this design. From my experience, backing the rubber fender washer with a steel washer dramatically reduces the lifespan of the seal. The impact of the plunger head causes "cookie cutter" action around the edges, eventually shredding the seal. It's why I replaced the washer in the compact plunger head of the SNAP-4 with 1/4" of an endcap: the plastic is just softer and rounded enough that it greatly reduce plunger seal damage. PVC backed seals last me at least a season. Steel backed didn't last me a war.

Another question: did adding the steel increase overall mass?

[rork]

It's all about the parts you use. My designs all use a 1"x1/2" bushing nested directly in the end of the pressure chamber, and I really can't recommend this method enough. The steel washer is wider than the rear of the bushing, so you get a great seal and no rubber damage. Zaxby's SNAPbow was rebuilt a few months ago with the correct washer, and I recently replaced the worn-out catchface with a new one after a full summer of use in assassin games. The rubber washers were fine, and I slapped 'em right back on.

Edit: Also, the padding washer helps with durability, while adding negligible mass.

I would say that the mass is about the same, maybe slightly less, with noticeably less friction.

Edited by rork, 05 December 2009 - 12:27 PM.

[Wes7143]

Another option to add, here for durable seals, is the use of grommets, rather than washers. I've done it a few times, using two large metal washers, a grommet fit to the plunger tube, and some washers to go inside of the grommet to keep it centered (whatever will fit).

Here's a photo (yeah, it's a crossbow, but it'll work in anything, really).

It's been in use for awhile, and I've seen no sign of wear.

[Carbon]

rork, on Dec 5 2009, 11:19 AM, said:

It's all about the parts you use. My designs all use a 1"x1/2" bushing nested directly in the end of the pressure chamber, and I really can't recommend this method enough. The steel washer is wider than the rear of the bushing, so you get a great seal and no rubber damage. Zaxby's SNAPbow was rebuilt a few months ago with the correct washer, and I recently replaced the worn-out catchface with a new one after a full summer of use in assassin games.

Cool, twp problems solved at once: cookie cutter and catchface. I salute you!

[umpshaplapa]

Would the wing-nut slamming into the front of your plunger tube eventually become a problem?

[rork]

The wingnut never touches anything. It lands inside the opening of the bushing.

[minsc]

rork, on Dec 5 2009, 12:19 PM, said:

It's all about the parts you use. My designs all use a 1"x1/2" bushing nested directly in the end of the pressure chamber, and I really can't recommend this method enough. The steel washer is wider than the rear of the bushing, so you get a great seal and no rubber damage. Zaxby's SNAPbow was rebuilt a few months ago with the correct washer, and I recently replaced the worn-out catchface with a new one after a full summer of use in assassin games. The rubber washers were fine, and I slapped 'em right back on.

Edit: Also, the padding washer helps with durability, while adding negligible mass.

I would say that the mass is about the same, maybe slightly less, with noticeably less friction.

First off, I really like this design, so if it means anything, props from me.

Couple questions though:
1. Did you get the nylon washer and parts from Mc Master? I was wondering if they're available there/what the part humbers were, since I'm planning on getting some springs anyway.

2. How did you attach the head to the rest of the plunger rod?

3. I'm building a similar design, but with 1 1/2 in pvc. Do you think the same metal washer combo would work even though the trigger pin would have to be longer? I haven't made a homemade yet, but I'm concerned with the durability of the clothespin trigger design.

4. Do you notice any wear on the epoxy putty ramp? Everytime I've mixed it, it still retains a level of softness and moldabilty long after it should have cured. I may not be mixing it enough though.

Edited by minsc, 11 December 2009 - 11:12 PM.

[rork]

1: All the parts for this came from Lowe's. The only thing on my SNAPs that doesn't is the spring.

2: drill a hole, use a pin or 2 screws.

3: 1 1/2" will probably be difficult to find appropriate rubber washers for. You can just upsize to 1 1/2" steel washers for the head, though.

4. the only way there's a bit of wear on the epoxy is if you use too much; It's a bit of a self-adjusting design that way. Epoxy putty is quite durable, but you DO have to knead the hell out of it.