JSR wants a lathe/mill thread -> JSR buys Sherline

[jackssmirkingrevenge]

First I know nothing about hybrid and cartridges... but... I want to learn!
In the meantime this little ball just waiting to fall down was bothering me.

There seems to be some lack of appreciation for the forces involved, I want to take this to 25x or so, which means the disk needs to reliably contain a pre-ignition pressure of 365 psi or so

1) Over-engineered just as I love it. More fun to machine too

How do you cut the female thread and still leave the lip that presses against the disk?

then I thought... threads are not JSR's best... so... let's remove them!

My original design was made with this in mind - cutting a female thread presented no problems, and as to the male thread, it's a question of cutting a thread in a length of rod then cutting it into sections, I think I can manage it. That way, you cut the problematic male thread once and use the result for multiple cartridges.

2) Why not using a o-ring simply to tighten the disk around?

It will pop off at very low pressure. Also, what would the fantastic burst disk material be? Ah, mylar? hmmm...

3) and 4) are just variations with a ring helping the compression.

That's much better, but again, you're stuck finding a suitable material for the burst disk. How would you cut the o-ring groove in 3)?

5) And then ... why not a simple piece of adhesive tape? Too ghetto? Surely it has been done before!

*1cm pump stroke* *pop*

If cutting an o-ring groove, this would be a great option. The projectile would act as both "burst disk" for firing and "one way valve" for filling. Even better is to have the o-ring sandwiched in a threaded fitting to make it adjustable ^TM

The o-ringed endplug centres the base while insulating it at the same time, allowing the spark gap to be effective.

[LeMaudit]

my lathe spending got blown this morning on http://www.bikes.com.au/p/1208638/2011- ... -1200.html

But... but... no motor!?

how would shipping from the US be?

I don't sell anything Ask a retailer. Sherline list a lot of them on their website. And there's some in Australia too... for example... Sherline Australia

If I can upgrade the 8 inch, I'll go with it

If you care about my opinion, I think it is not a good idea. I've made a little photo comparison about the real useful lengths between the two sizes. The short one is really short. You sure will have fun with it, but the price difference is "only" $100, and this include zero resettable handwheels that the short bed don't have by default. So it really is a $45 difference. But it's your choice after all. Mind also that you will not have any accessories for that price, not even a chuck. Only a lathe dog. You should really look at their "packages" for a enjoyable startup. Paying twice the shipping charges is not a pleasant idea.

There seems to be some lack of appreciation for the forces involved, I want to take this to 25x or so, which means the disk needs to reliably contain a pre-ignition pressure of 365 psi or so

There was... and it was a long day
25x... right...

How do you cut the female thread and still leave the lip that presses against the disk?

Magic? Or a boring bar + bottom tap... or this nice and shiny thread cutting accessory you don't have... yet!

My original design was made with this in mind

Yes your original design remove the difficulties, no question about that. It was just this little falling ball that itched me... but then again... a piece of tape in front of it... I don't know why... I'm feeling ghetto... too much shininess with the pengun maybe... my next project could be a zombie killer machine...

It will pop off at very low pressure. Also, what would the fantastic burst disk material be?

For 365psi and say 4.5mm ammo, it's about 4 kg/9 pound pressure, right?
Is it really that fantastic? All right... I know nooothing...

How would you cut the o-ring groove in 3)?

The boring tool.

But it will not be that square. Or the threading tool maybe:

Or a miniature "real" o-ring grooving tool but they are expensive. I think I would grind my own for a project of making a bunch of those.
An other option would be a mill cutter on the rotary table.

The projectile would act as both "burst disk" for firing and "one way valve" for filling.

But the o-ring would have to resist that 4kb pressure on it...will it really?

why not a simple piece of adhesive tape?
*1cm pump stroke* *pop*

I have to give this a try with strong industrial tape!
... I did... all right... I'll return finish machining this next piece for the pengun. It's my first pneumatic thingy after all...

[jackssmirkingrevenge]

Magic? Or a boring bar + bottom tap... or this nice and shiny thread cutting accessory you don't have... yet!

No bottom tap either. I can work around it for now with my epoxied threaded section part plan

this little falling ball that itched me...

If it's a tight fit in the tube it won't be a problem - lead is softer than brass

but then again... a piece of tape in front of it... I don't know why... I'm feeling ghetto... too much shininess with the pengun maybe... my next project could be a zombie killer machine...

I told you - this exchanging of ideas is going to lead to an equilibrium!

For 365psi and say 4.5mm ammo, it's about 4 kg/9 pound pressure, right?
Is it really that fantastic? All right... I know nooothing...

Not really in terms of material strength, in this one a single layer of scotch tape held 400 psi easily for a 6mm hole. The question is holding it in place, and maintaining a seal after bending it, I doubt your design is up to it.

The boring tool.

*yawn*

see what I did there?

Too wide for a 5.5mm projectile...

An other option would be a mill cutter on the rotary table.

I see... something like these?

But the o-ring would have to resist that 4kb pressure on it...will it really?

Oh yes. I made a (unpublished) cartridge protoype with this system, first It wouldn't work because I was filling through a schrader in the cartridge, and as some air is lost until the projectile seals I could never get the mix right. When I made my fill rig I tried it out, problem was I squashed the o-ring a bit too much and at 20x it held the pellet so tightly that the whole plug blew out instead of the projectile being fired...

I did... all right... I'll return finish machining this next piece for the pengun. It's my first pneumatic thingy after all...

Good man

[LeMaudit]

I see... something like these?

Yup, something like the one on the bottom. Just insert the cutter in the hole, move a bit the table so the cutter dig into the metal, and make a full turn with the rotary. Then repeat if necessary.
That's an easy way to do very complex internal cuts. Told you the rotary would be useful, it's not only to cut dimples!

Dremel have a kinda cheapo cutter that could do I guess on brass or aluminum.
I never did that (grooving I mean) but I used other kind of cutters similarly. At the highest speed on the motor, cause Dremel cutters are made to cut because they rotate fast, not because they are sharp

If you don't have one of those dremel cutter, I do (oeuf-corse) and I could give it a try.

[jackssmirkingrevenge]

Egg Corsica?



Interesting. I think it's better to invest in the cutter than a dremely tool that will likely wear out fast anyway. Any eBay links

I was going to get started on a tentative burst disc prototype, but I'm off to a barbeque, damn social life!

[LeMaudit]

Don't spit on Dremel cutters They are crap only when you use them on a crap hand drill... like a Dremel

A Dremel cutter like that one is $5.25 on eBay, and about $9.99 on your favorite store.

With it you should be able to make a groove max 25mm from the hole's edge (hole's diameter min 9.6mm), max 3mm deep and min 1mm thick. You'll have to pay $50 or so to have the same from machinist supplies I think. If not please give me some links and I'll buy

Cutting aluminum and brass, the Dremel cutter should be okay. If you are patient enough I'll try it for you. I need to do the same for my own experiments anyway. Don't forget you have a limited set of cutters right now, better group your next buyings or you'll spend a lot in shipping charges.

Now, a real carbide or fine HSS cutter, that's not in that price range!
Search for "Slot cutter" on eBay.
Remember you'll need a 3/8" max arbor to use it without additional accessories, and for very small ones, you'll need solid carbide ones.
For a nice selection and an idea of prices, look KBCTools catalog pages #204 to #209

[jackssmirkingrevenge]

Point taken, but:

With it you should be able to make a groove max 25mm from the hole's edge (hole's diameter min 9.6mm), max 3mm deep and min 1mm thick.

... doesn't help me to slot for a 5.5mm projectile.

There'sthis one but it's still 7mm min diameter...

[Zeus]

If I can upgrade the 8 inch, I'll go with it

If you care about my opinion, I think it is not a good idea. I've made a little photo comparison about the real useful lengths between the two sizes. The short one is really short. You sure will have fun with it, but the price difference is "only" $100, and this include zero resettable handwheels that the short bed don't have by default. So it really is a $45 difference. But it's your choice after all. Mind also that you will not have any accessories for that price, not even a chuck. Only a lathe dog. You should really look at their "packages" for a enjoyable startup. Paying twice the shipping charges is not a pleasant idea.

I certainly care for your opinion, I know very little of lathes, and you've got quite a mastery over the machine I'd like.

So I'll certainly get the 17" bed, but now deciding between the two packages is the concern.

Basically, the 4410B lathe package, or the 4410C listed here?

Is the compound slide and thread cutting tool worthwhile, or would the other package suffice?

Many thanks for your advice.

Edit: Formatting

[jor2daje]

Jack I would personally just do it on the lathe, grab a hss blank and just shape your own internal groover (course I don't have a rotary table yet, things may change)

[jackssmirkingrevenge]

So I'll certainly get the 17" bed, but now deciding between the two packages is the concern.

I bought the 4410A package and everything else separately as per LeMaudit's advice. I'm currently cutting threads by hand which is a bit of a pain in the arse, so I can see the threading attachment being useful. As to the compound slide, while it looks convenient in practice you can probably do without it.

Jack I would personally just do it on the lathe, grab a hss blank and just shape your own internal groover (course I don't have a rotary table yet, things may change)

And pointers to what grinding setup would be ideal for making my own tools?

[LeMaudit]

doesn't help me to slot for a 5.5mm projectile.

Oh, right. That small, hey...

you've got quite a mastery over the machine I'd like.

Not really I know a bit, fiddling around since a long time.. and I don't mind sharing the little knowledge I have.

compound slide and thread cutting tool worthwhile

You can rotate the head to create taper on short rods, or low angle taper on long rods. If you want to create an angle, say 30° at the end of a 6 inch rod, then you'll need the compound attachment. If you limit yourself to making tapers on short length only (like the pengun nose), then you can do without it.

The thread cutting tool, I have it but didn't have the chance to unpack it out of its box yet So I don't have an opinion on it. What I know is that threading something bigger than 3/8" to 1/2" is somehow a challenge with manual tap/dies. If you want to make large diameter threads I think you would need it. But you can do other kinds of attachments too, like steel pins, bolted, etc... it really depends of what you have in mind.

I personally did without a threading attachment for years, but I used the compound right from the start. Now that I machine bigger stuff and want threading, it's different.

I bought the 4410A package and everything else separately as per LeMaudit's advice.

JSR wanted both a lathe and a mill on a budget, so yes I picked what seemed essential to start working using my knowledge of the tools. In Zeus case, as he want only a lathe, it is different.

And pointers to what grinding setup would be ideal for making my own tools

You need HSS blanks 1/4", and a bench grinder. You will need a quality grinding wheel, so you may find a cheap grinder, but I suggest you buy a separate wheel too. Of course it depends of what you find.
For fine tuning and shaping, you can grind HSS with a Dremel or a fast hand drill and quality diamond bits.
If you are tempted to stick a grinding bit on your lathe or mill, don't. You don't want abrasive dust inside the threads.

Also, a bench grinder generate nasty dust, be aware of that.

[jackssmirkingrevenge]

You need HSS blanks 1/4", and a bench grinder. You will need a quality grinding wheel, so you may find a cheap grinder, but I suggest you buy a separate wheel too. Of course it depends of what you find.
For fine tuning and shaping, you can grind HSS with a Dremel or a fast hand drill and quality diamond bits.
If you are tempted to stick a grinding bit on your lathe or mill, don't. You don't want abrasive dust inside the threads.

Also, a bench grinder generate nasty dust, be aware of that.

Does the grinder need to have any particular attachments though, like a tool rest?

But you can do other kinds of attachments too, like steel pins, bolted, etc... it really depends of what you have in mind.

Speaking of pins, here's what the cartridges would look like. Avoids the thread, but not as simple to reload.

[LeMaudit]

Does the grinder need to have any particular attachments though, like a tool rest?

I think they all have more or less something... more or less crappy, depending on the original price. I'm really not a specialist here, I use carbide tollbits just NOT to have to use the grinder!

mine looks like that:

Craftsman 6" Bench Grinder with Lamp

It's not even installed in the workshop This let you know how often I needed it.

The easy alternative is to buy a miniature carbide cutter for o-rings. You'll find plenty of usages for it. Unless you really prefer to build tools and cutters instead of building cartridges.

[ramses]

Does the grinder need to have any particular attachments though, like a tool rest?

It helps. A lot. I've tweaked lathe bits with an angle grinder before, with the bit clamped in my toolpost before, but it was damn scary. I've seen a reamer ground without a tool rest, and it didn't look easy or safe. The grinding wheel happened to be attached to a surface grinder. My Foreman just didn't want to walk over to the bench grinders I guess...

[jackssmirkingrevenge]

double post...