Search found 169 matches

by mrfoo
Sat Aug 08, 2020 1:07 am
Forum: Hybrid Cannons
Topic: Cooking up a little something...
Replies: 79
Views: 13246

Re: Cooking up a little something...

Wow, missed that update, came back here from the link you posted elsewhere. 100% success indeed. 1067fps for a golf ball means you're basically being maxed out by the shock wave, i.e you're hitting the sound barrier. This makes me wonder what could be done with a streamlined projectile of the same c...
by mrfoo
Sun Jul 19, 2020 1:59 pm
Forum: General How-To & Discussion
Topic: JSR's workshop chronicles
Replies: 32
Views: 6571

Re: JSR's workshop chronicles

that is my understanding, yes.
by mrfoo
Tue Jul 14, 2020 12:44 am
Forum: General How-To & Discussion
Topic: Short question topic
Replies: 1484
Views: 96721

Re: Short question topic

His explanation of how it works is dead wrong, the pressure in the two chambers will always equalise. The principle at work is exactly the same as that of a QEV, the force exerted on the piston at the "bulb" end is gas pressure * piston cross sectional area, and at the strut end it's gas pressure * ...
by mrfoo
Mon Jul 13, 2020 3:38 am
Forum: Off-Topic Hobbies
Topic: Interesting To Know
Replies: 3
Views: 252

Re: Interesting To Know

Interesting, but if you're talking about "shop sci-sc-sci-science!", you probably should spend the first part of the video talking about how much "power" you're getting from a screw press. Also, he keeps going on about friction being the killer, but it's clearly not, as shown by his grease test. In ...
by mrfoo
Sun Jun 14, 2020 4:12 am
Forum: Ammo & Parts
Topic: Ideas for biodegradable cannon-balls
Replies: 15
Views: 3251

Re: Ideas for biodegradable cannon-balls

I'd guess a simple flour / water paste would work. Plain flour, though, not self-raising.
by mrfoo
Fri Jun 12, 2020 6:10 am
Forum: Hybrid Cannons
Topic: Port size vs performance
Replies: 8
Views: 861

Re: Port size vs performance

Quite. There's going to be a point of diminishing returns where, for a given design and geometry, going bigger will eventually slow the piston down. There's a lot of benefit to be had, for a port that's smaller than the barrel, from profiling the edges of the port, both chamber side *and* barrel side.
by mrfoo
Mon May 25, 2020 5:51 am
Forum: Combustion Cannons
Topic: I was hoping for some feedback on my oxy-propane combustion cannon.
Replies: 7
Views: 795

Re: I was hoping for some feedback on my oxy-propane combustion cannon.

Personally, I wouldn't use PVC for anything involving compressible fluids at pressure, certainly not for combustion chambers, and doubly not so for anything involving oxy-gas mixtures. But that's just me, I like to keep the parts of my body complete and attached where they are. For air and propane, ...
by mrfoo
Mon Apr 27, 2020 1:18 am
Forum: BB, Airsoft, and Pellet Guns
Topic: Help with making a diy blowback system
Replies: 7
Views: 1066

Re: Help with making a diy blowback system

Boyle's Law tells us that, for a constant temperature, pressure is inversely related to volume, so for a fixed quantity of gas, if we reduce the volume by a factor of 2, we raise the pressure by a factor of 2. So, if we assume you have a 100mL chamber at atmospheric pressure, and you want to raise i...
by mrfoo
Tue Apr 14, 2020 1:00 am
Forum: Off-Topic Hobbies
Topic: "Offtopic-posts-topic" NSFW
Replies: 6630
Views: 260705

Re: "Offtopic-posts-topic" NSFW

Machine tools might possibly be valid reasons for divorce.

Selling my machine tools after a divorce would be a valid reason for "disappearance"
by mrfoo
Sun Apr 12, 2020 2:59 am
Forum: Off-Topic Hobbies
Topic: "Offtopic-posts-topic" NSFW
Replies: 6630
Views: 260705

Re: Re:

CX500 That's the "custom" maggot, right? Do like those reverse comstars. The standard CX500 was the ubiquitous super-cheap courier bike in London in the late 80's / early '90s. Known as the "plastic maggot", and usually brush-painted matt black (mine certainly was), they were loved and hated in equ...
by mrfoo
Tue Mar 17, 2020 1:41 am
Forum: Off-Topic Hobbies
Topic: Waste oil burner
Replies: 17
Views: 3889

Re: Waste oil burner

Tim Taylor the character in "Home Improvement", or Tim Taylor the producer of the UK's archaeology programme "Time Team"?

Either would work.
by mrfoo
Mon Mar 16, 2020 2:32 am
Forum: General How-To & Discussion
Topic: Short question topic
Replies: 1484
Views: 96721

Re: Short question topic

Porting and piston form is going to be important to get air out of a short, squat, cylinder into a long, slender, barrel in a hurry. The big issue is, IMO, going to be changing the direction of the air, as such I'd probably go for a conical piston face mating to a conical cylinder end, with highly r...
by mrfoo
Fri Mar 13, 2020 4:02 pm
Forum: General How-To & Discussion
Topic: JSR's workshop chronicles
Replies: 32
Views: 6571

Re: JSR's workshop chronicles

Is that really an issue though? Would be for me. 52mm high (sensor + scale) seems to be pretty much standard, and is more than half the 102mm centre height on my lathe. Wherever you put 'em (and you're really only got 2 choices), they're overhanging, interfering. Simply won't fit on my machine, whi...
by mrfoo
Fri Mar 13, 2020 11:00 am
Forum: General How-To & Discussion
Topic: JSR's workshop chronicles
Replies: 32
Views: 6571

Re: JSR's workshop chronicles

That's more than serious enough for any hobbyist who isn't doing, for example, watch parts. The majority of the more inexpensive glass scales are, IIRC, accurate to 5 microns. The only real issue is size; they are a bit "phat". For metric work, it's possible, with a bit of trigonometry, to use your ...
by mrfoo
Fri Mar 13, 2020 4:38 am
Forum: General How-To & Discussion
Topic: JSR's workshop chronicles
Replies: 32
Views: 6571

Re: JSR's workshop chronicles

The conversation got me looking around...might have to loosen the wallet a little and up the game a touch...DHL shipping is FREE?? Odd...but welcome. https://www.aliexpress.com/item/32844760798.html?spm=a2g0o.productlist.0.0.1f77e078Ulzxga&algo_pvid=424a8b8d-51a6-4e9c-9d58-ccce3a53415d&algo_expid=4...