4 replies to this topic

[AnOoB]

I have been wanting to make a homemade blaster for a really long time and decided to begin.

Almost immediately i came to the point that i failed to understand the sizes of all the parts.

I hope someone is willing to help me out and explain how this works.

 

link for writeup: nerfhaven.com/forums/topic/20296-snapbow-mk-v-revised/

 

i´m sorry for my bad english, i am not a native speaker.

 

 

 

please explain this:

[Meaker VI]

Sorry buddy, nearly every writeup on this site is dependent on Imperial units, and actually cannot be simply converted. This is because we're so dependent on Imperial parts sourcing: our pipe, materials, and hardware are in inch sizes, and metric equivalents may or may not correlate. It makes it even harder that our pipe sizes are named based on imperial units, but due to differing sizing standards, not usually the same ID/OD as similarly named pipe used under a different standard (i.e.: 1/2" copper pipe, 1/2" CPVC pipe, and 1/2" PVC pipe are not the same size, despite all being plumbing pipe, PVC/CPVC being plastic pipe, and Copper/CPVC being supply pipe).

You're on your own finding out what metric parts actually go together the way we'd put them there, but we can guide you as to what should work. Here's a typical Imperial PVC pipe dimension chart (Oh yeah, there are also different schedules of PVC, which have different wall thicknesses. We usually only use schedule 40 and 'thinwall' 200-psi which is schedule 30, I think):

 

 

1-1/4 schedule 40 (or similar polycarb tube) is what we usually use for plunger tubes, and is the only size that really matters. In metric, it'd have an OD of 42.164 mm and an ID of 34.544 mm. All the other pipe and hardware sizes we use are because they nest with that and nesting won't work the same way with metric sizes as it does with imperial sizes.

 

All that said, SGNERF does do metric homemades. Here's one, here's a more advanced version that looks awesome IMO and I'm a little jealous it's in metric. You might be able to find appropriate rubber washers where he custom builds his.

[The2ndBluesBro]

Basically what Meaker VI said. If I were you, I'd contact the Australians over at http://oznerf.forumotion.com/or on one of the various facebook groups. Many of the screw sizes listed are simply that size due to ease of availability and metric screws like M3 or M4 size can be substituted for them easily, for example to attach the front bushing. Most of the homemades people have made are similar to the AK-47 in that respect. Very loose tolerances, on screw size at least. Just look for a screw that's about the right size. However, for things like the rubber washer, you're basically screwed unless you import them or make your own. Finding something else that fits (drain plugs?) is probably your best option there.  

Edited by The2ndBluesBro, 05 February 2016 - 01:48 PM.

[AnOoB]

Thank you guys,
I'm definitely going to look up those metric writeups.

[Meaker VI]

Many of the screw sizes listed are simply that size due to ease of availability and metric screws like M3 or M4 size can be substituted for them easily

Add to this, the screw sizes don't matter at all, as long as they do three things:
1) They are long enough penetrate what they need to
2) Not so long that they penetrate too far
3) Are thick enough to resist breaking

Which are usually #6 or #8 and 1/2" long around here. Apparently #6 is M3.5 and #8 is M4. I usually use sheet metal screws, which have a courser thread to bite into the plastic better. 1/2" is about 13 mm.
 

Finding something else that fits (drain plugs?) is probably your best option there.

The parts we use are largely plumbing related, but some are just parts. Rubber washers are just rubber washers, see if you can source them in metric sizes that fit your material ("fit" as in, "fit tightly" - the washers we use are bigger than the ID of the pipe they go in), the cup seals and bushings and etc. should also *exist* in metric sizes, I just don't know where you'd source them or if they'll fit metric pipe as well as the imperial parts fit the imperial pipe.