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Short question topic

A place to ask general spud cannon related questions.
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Unread postAuthor: wyz2285 » Sun Mar 03, 2013 12:48 pm

200 mm is the distance between 2 centers, so if I'm just turning a rod, the rod can be max 200 mm long and around 80mm diameter?
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CpTn_lAw wrote::D "yay, me wanna make big multishot pnoob with 1000 psi foot pump compressor using diamond as main material. Do you think wet bread make good sealant? " :D
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Unread postAuthor: jackssmirkingrevenge » Sun Mar 03, 2013 12:53 pm

Pretty much, but if you want to drill a hole in the rod you have to subtract the length of the drill.
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Unread postAuthor: wyz2285 » Sun Mar 03, 2013 12:56 pm

Got that, thanks.
Too bad the sell is end, but probably I can find another one and if everything goes fine I'll be a lathe+mill owner :)
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CpTn_lAw wrote::D "yay, me wanna make big multishot pnoob with 1000 psi foot pump compressor using diamond as main material. Do you think wet bread make good sealant? " :D
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Unread postAuthor: wyz2285 » Sun Mar 03, 2013 2:21 pm

Found this, from the price and location I'd say it's crap. But I can afford it right now, also I'm totally new to machining so does it worth for me to buy and use it to warm up my skills before I buy a decent one
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CpTn_lAw wrote::D "yay, me wanna make big multishot pnoob with 1000 psi foot pump compressor using diamond as main material. Do you think wet bread make good sealant? " :D
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Unread postAuthor: dewey-1 » Sun Mar 03, 2013 2:59 pm

That thing is more of a TOY than a TOOL.
Save your money and apply towards a real lathe/mill like JSR has.
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Unread postAuthor: wyz2285 » Sun Mar 03, 2013 3:28 pm

I know, but I'd like to know some basics about machinery so I won't break anything when I buy a real one. 130 euro doesn't make a big difference when I'm saving >1000 euro for a real one and if it prevents me from getting hurt r damage the machine I don't mind. Can it at least machine aluminum and nylon? Like the internals of a hammer valve and some blow forward bolt or small pistons?
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CpTn_lAw wrote::D "yay, me wanna make big multishot pnoob with 1000 psi foot pump compressor using diamond as main material. Do you think wet bread make good sealant? " :D
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Unread postAuthor: PaperNinja » Sun Mar 03, 2013 3:29 pm

I'm having a lot of trouble firing my hybrid, I think I might have the wrong amount of propane. I know it's supposed to be 4% ish of propane, does that mean I can do it based on pressure alone?

I mean, if I pump to 60 psi, then there's 74.7 psig of air in the chamber. Can I just add 4% * 74.7 of propane to fire?
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Unread postAuthor: MrCrowley » Sun Mar 03, 2013 4:35 pm

PaperNinja wrote:I mean, if I pump to 60 psi, then there's 74.7 psig of air in the chamber. Can I just add 4% * 74.7 of propane to fire?

Read over 'part 2':
http://www.spudfiles.com/forums/hybrid- ... 13602.html

PaperNinja wrote:I'm having a lot of trouble firing my hybrid, I think I might have the wrong amount of propane. I know it's supposed to be 4% ish of propane
I'm not surprised that you can't get it to fire since you're calculating in terms of "-ish". You're making a hybrid, not a spray and pray.

Get a 0-15PSI gauge with at most 2% F.S. accuracy (or a 0-30PSI gauge with 1.5% or lower F.S. accuracy). If you read the above link, you will notice that you need 0.64PSI of propane for each mix. If you're doing a 5x mix, measure out 3.2PSI of propane in the chamber and then add 4bar of air (~58.8PSI).
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Unread postAuthor: PaperNinja » Sun Mar 03, 2013 5:24 pm

I'll probably have to get a better gauge in that case :x

I was hoping to meter, instead of based on mix numbers, on the air I put in. I want to do it like that because my shock pump gauge is not very precise (small dial that goes to 600 psi). So if I put in 250 psi, can I just put in 264.7*0.04 = 10.58 psi of propane? I'm thinking no, because that has a final pressure of 275.28 psi, and 10.58 is only about 3.84% of that.

I hope this works as I think it does:

(P = propane pressure, A = air pressure)

P should be 0.042 * (P+A) for it to be 4.2% of the final mix, so P = 0.042*(P+A)

A isn't really the air pressure in the chamber, A+14.7 is, so

P = 0.042*(P + A + 14.7)

P = 0.042*P + 0.042*A + 0.042*14.7

0.958*P = 0.042*A + 0.6174

P = (0.042*A + 0.6174)/0.958

So when A is 250, P = 11.604 so the propane is 4.2% of the total pressure.
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Unread postAuthor: MrCrowley » Sun Mar 03, 2013 6:04 pm

PaperNinja wrote:Does the air need to be as accurate as the propane, or is there a little more wiggle room? I'm guessing it needs to be just as accurate right?
I'm sure there's more room for error with the air (I assume due to the proportions) as a gauge that reads 0-140PSI with an error of 2% F.S. may read 135PSI when the real pressure is closer to 138PSI yet a hybrid will still fire if you're off by a few PSI in air. With the fuel, however, if you're off by 3PSI you're in a completely different realm of mix.

However, I assume both the fuel and air need to be as accurate as each other in terms of proportions. So if the fuel mix can be off by +/- 0.25PSI for a 10x mix (0.25PSI is 1/26 of the fuel mix) and still ignite when the correct amount of air is in the chamber, the same may hold true for the air (i.e. the air can be within +/- 1/26th of its required pressure and still fire if the fuel has been measured correctly).

The above numbers may be wrong and a hybrid with a fuel or air mix off by 1/26 might not fire but I think there would be reasoning similar to the above that holds true and a more chemistry-minded member may be able to fill you in on the science behind it.
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Unread postAuthor: jackssmirkingrevenge » Mon Mar 04, 2013 1:32 am

dewey-1 wrote:That thing is more of a TOY than a TOOL.
Save your money and apply towards a real lathe/mill like JSR has.


Listen to dewey on this one. I was considering that same device in the beginning and now realise it would have been a mistake.

If you want something to practice on, fair enough it's not *that* expensive, but forget any type of metal, at best you can do balsa wood and maybe some plastics.

Typical review: http://jbwid.com/gij36.htm

It's a toy.

I'm having a lot of trouble firing my hybrid, I think I might have the wrong amount of propane. I know it's supposed to be 4% ish of propane, does that mean I can do it based on pressure alone?


JSR recommends syringes<sup>®</sup> ;)

MrCrowley wrote:The above numbers may be wrong and a hybrid with a fuel or air mix off by 1/26 might not fire but I think there would be reasoning similar to the above that holds true and a more chemistry-minded member may be able to fill you in on the science behind it.


If you want to know by what percentage you can afford to be off, consult the list.
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Unread postAuthor: Labtecpower » Mon Mar 04, 2013 5:19 am

Found this, from the price and location I'd say it's crap. But I can afford it right now, also I'm totally new to machining so does it worth for me to buy and use it to warm up my skills before I buy a decent one


It has plastic parts, not even suitable to machine most polymers.

Try to make a .5 mm cut in plastic with a toolbit and your bare hands, you'll be amazed of the power needed.
Machining won't be any fun on that lathe, better save your money to buy some tools :D
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Unread postAuthor: wyz2285 » Mon Mar 04, 2013 10:25 am

It has plastic parts, not even suitable to machine most polymers.

I know, but exactly how many part is made by plastic? It says can machine up to aluminium, and for now 12mm dia aluminium rod and nylon are the main material I use on my drill press.
If this thing can machine parts of a pen gun, internals of a hammer valve, some bolts, I'd buy it. Now, what I don't know is if that's possible with is lathe?
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CpTn_lAw wrote::D "yay, me wanna make big multishot pnoob with 1000 psi foot pump compressor using diamond as main material. Do you think wet bread make good sealant? " :D
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Unread postAuthor: jackssmirkingrevenge » Mon Mar 04, 2013 12:20 pm

wyz2285 wrote:It says can machine up to aluminium


... and they say Prius can go from nought to sixty in 3 seconds*

*if you push it off the edge of a cliff

Read the reviews, and see the experiences of those who tried to use it with aluminium.
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Unread postAuthor: Labtecpower » Mon Mar 04, 2013 12:29 pm

I know, but exactly how many part is made by plastic? It says can machine up to aluminium, and for now 12mm dia aluminium rod and nylon are the main material I use on my drill press.
If this thing can machine parts of a pen gun, internals of a hammer valve, some bolts, I'd buy it. Now, what I don't know is if that's possible with is lathe?


It looks pretty much like it is all plastic :D

The chuck looks like aluminium or some die-cast stuff zamak alloy..
Verything is too weakly executed to machine anything above balsa I think, if you try to machine aluminium you have a chance of horribly chattering tools making rough cuts, if they even cut at all.
When I machine at the unimat I feed 1mm. of aluminium on every cut, with a cutting speed of about 600 rpm for a 35 mm. piece. Automatic feed between 0,06 and 0,012 mm. per rotation of the chuck.
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