Are you using metric or SAE stuff to build rockets?

[dr wogz]

I forgot nothing, but I figured enough was enough. I stopped before going into copper water pipe - er, tube - and if hydraulic line tubing is different yet I 1) didn't know that, and B) wouldn't be a bit surprised. (Didn't know is a different thing from forgot.)

And Paul, yes my point also was to point out how silly some of these are and have a laugh. For the home owner looking at a toilet line and saying "That's 1/4"?", I had the opposite problem. I got used to pipe sizes and routinely understated the size of other things. "Looks about like 3/4" pipe, so I guess it's 3/4 of an inch." Now that I've learned better, my mental reference for 3/4" is the thickness of a 1× board.

And why is a long cylinder used to carry water called a pipe if it's iron and a tube if it's copper? And the same (well, nearly the same) piece of iron is called conduit if it's got wires inside.

It's a mad house! A mad house!

thanks for the chuckle!! (i did actually chuckle a bit as I read your post.. the 'I totally agree with you' chuckle!)

We've actually had to make & enforce the distinction here where I work, make sure we call up either 'Pipe' or 'tube' (or hose and flexible tube) even!!

Of course, when I first started here (8yrs ago) i thought: "Man, these ovens sure have a lot of plumbing.."


(I work here, designing & developing these.. And thank you for buying a chicken!!! (and pizza)
https://www.hardt.ca/

 

[Nytrunner]

I have 1.5 and 2.25 grams of BP in my 15lb rocket that's 5.5" wide, 9' tall, and has a 54mm motor mounts (with 6mm thick "1/4" ply fins!)

if you can't get a 2.6" tube but a 66mm is on sale,

Hah!

Wire gauge is different for copper, steel, and piano wire (a.k.a. music wire) even though that last is also steel.

I read a fascinating account talking about how each progressively smaller numbered die relates to how much the wire diameter can be reduced in one step without being compromised. Since that's related to material properties, the gauge #s are different across them

 

[jqavins]

That makes, um, sense?

 

[Javelin]

Nice writeup! The US definition of the inch is now exactly 25.4 mm, and (I think but may be wrong) other imperial length units are defined according to that. That is, the yard is still defined as 36 inches. (At least that's how I and coauthors describe it in Chemistry for Changing Times 15th ed ).

FWIW technically, SI (French, Systeme International) bases all measurements (and other derived units) solely on the seven base units. A diameter, whether atom or Sun, is expressed in meters. Mass of a flea or a mountain in kilograms. Time is in seconds, etc. A joule is one (kg m^2)/s^2 and is the only energy unit used in SI. SI makes unit issues per se almost impossible. Of course it's only used in the sciences, and even then not by every scientist. Prefixes (i.e., metric system) size the unit down or up and are far more convenient for most measurements.

1 kilosmile = 1000 smiles
Terry

Good summation of how we collectively screwed up for likely what was screwy reasons. Rather than continue using the inch as the standard unit of length, we was sold a bill of goods, to better sell it to many third world countries, who wanted money promised to retool factories. Now I have a set of deep sockets that fits both, but mostly you need two sets of everything, and screws and bolts are confusing and not interchangeable.

Oh well my Javelin Tosser is turning out all based on English measurements, although today I'll use metric bits in my Dremel to cut slots for fins and eventual wings, so the launched items resemble small gliders. 10/11ths of a foot is the Barbie size length, and fits neatly in a three ring binder.

Mostly the launcher is a catapult that drops a ten pound weight approximately 30 inches, with a pivot axle at 16 inches from the center of mass. Using a 6 foot aluminum bar generates 3.3 g' of acceleration so it launches at about 28 MPH, with an adjustable launch angle, but hope pi/8ths works well. The weight falls at a rate of 32' per second^2 in a straight line. It actually follows a circular path so I use g' to represent g prime, and the other end is a simple ratio proportion calculation. For larger spaces, the bar can be lengthened to launch at 4 or 5 g's. The table height also adjusts from 22 to 36 inches, so should cover a wide selection of launch venues.

Actually it was my dad that explained the change-over when he worked for Sperry Univac and helped build computers for the Apollo space missions.

 

[Javelin]

Actually tubing vs pipe is more a diameter thing not a material based. Smaller diameters of pipe are commonly called tubing and larger diameter are pipe. However that changes when the purpose changes from being a vessel being structural, now tubing is more like a round structural member.

Currently I use round 1/2 inch PVC for the fuselage. Since it's structural it's then proper to call it PVC tube.

 

[beeblebrox]

Just like screws should be listed with their thread major and minor diameters, and we should all move on from this pointless "number whatever" relic.

I agree, but Joe Handyman that thinks he is a construction wizard because he built horse head bookends in high school shop would be confused...lol

I don't know the diameter(s) of a BT-70 (in milimeters or inches) but I do know what one looks like. It's a handy verbal shorthand.

Hope the spreadsheet is useful, data from eRockets with a couple others thrown in that I was aware of.


No, I don't believe you. I don't know what change was made in 2013, but the inch has been defined as 25.4 mm for a lot longer than that. (Or maybe it's the yard that's defined, and the inch is 1/36th of it.)

Here is some helpful stuff...

 

[beeblebrox]

I prefer metric, as most of the 3D models I end up finding on thingiverse or whatever are designed in metric, and slicer programs are set up for metric. Stocking up on one type of fastener is enough too... Also...I like the fact that metric nuts are smaller in ratio with the screws that fit them.

 

[OKTurbo]

Mechanical Engineer and car guy here. I grew up in the 70’s and 80’s which meant my first mechanical experiences were with old 60’s American cars. My brain works best in SAE terms, but I adapt. My 87 Grand National has an annoying assortment of sae and metric fasteners. I also used to work on old British motorcycles, my last one was a 72 Triumph Trident.

I have all the tools! The Metrinch tool set is handy for all flavors. I even have a set of Whitworth spanners....how many can say that! It gets fun sorting out all the sockets once the job is done.

 

[OverTheTop]

Metrinch are great.

And I have a set of Witty spanners .

 

[Anthony Claiborne]

All the software code I write to support my rocketry addiction takes any form of input you specify, SAE, metric or (for body tubes) Estes BT standards. I never convert - I let the code do it. Internally, all my programs use metric, of course.

 

[JDcluster]

SAE 99% metric for 3d printing. Try finding metric drill bits at any of the big box stores.....

 

[OzHybrid]

Just because something is a Standard, doesn't make it standard. Try finding an M11 left hand thread nut.
Each standard, metric and imperial, has a range of readily available sizes. Provided that available range doesn't compromise what you need to achieve use whatever you want.

Take into account availability where you want to launch and what might be available there. When you're standing at the launch rail and need a special screw that you've dropped and no-one else has, make sure you've got a spare...

Having said that, I prefer Metric. And my 3D printer works well in Metric....

If you're using that standard Metric range, it reduces the number of screw sizes you have to stock. I have a box of M2, M3 ,M4, M5 for rocketry. Plus a selection of other non standard range screws.
For a launch I put a selection of what's needed for the rocket in the range box. I normally create that BAG as I build. 6 for you, rocket, 1 for me, range box.

 

[rharshberger]

Just because something is a Standard, doesn't make it standard. Try finding an M11 left hand thread nut.
Each standard, metric and imperial, has a range of readily available sizes. Provided that available range doesn't compromise what you need to achieve use whatever you want.

Take into account availability where you want to launch and what might be available there. When you're standing at the launch rail and need a special screw that you've dropped and no-one else has, make sure you've got a spare...

Having said that, I prefer Metric. And my 3D printer works well in Metric....

If you're using that standard Metric range, it reduces the number of screw sizes you have to stock. I have a box of M2, M3 ,M4, M5 for rocketry. Plus a selection of other non standard range screws.
For a launch I put a selection of what's needed for the rocket in the range box. I normally create that BAG as I build. 6 for you, rocket, 1 for me, range box.

Off to the launch or bench fasteners boxes common for my rocketry needs (among others)...
Sorted and labeled by size, the ones on the end are not yet labeled but contain rail buttons and the means of attaching them in various ways. No metric as they are expensive and non-standard in MY fleet.

 

[OzHybrid]

Off to the launch or bench fasteners boxes common for my rocketry needs (among others)...
Sorted and labeled by size, the ones on the end are not yet labeled but contain rail buttons and the means of attaching them in various ways. No metric as they are expensive and non-standard in MY fleet.

View attachment 431443

Metric screws are readily available on ebay as kits for the same price as any imperial screw. There is no price difference if you plan ahead and are talking about having stock in place for building.
An imperial tap and drill costs the same as a metric one if you are prepared to wait for it to be delivered.
Always remember if you want it at the right price you're going to have to wait. If you want it now, you're going to pay the price.

A rocket for me is a year project. With covid, that will be a 2 year project on this cycle.

Everyone's reason to be doing this hobby is different. If you're building a rocket this weekend or coming up to a deadline, use whatever you can get hold of that works for you and you've got spares of. I doubt anyone chooses screws based on a deep rooted philosophical necessity.

 

[OzHybrid]

Screw Philosophy.

If I choose Metric.

Any Metric size is the drill size for an exact fit.

Example:- Screw M4x0.7 pitch (standard coarse thread M4)
Drill 4.0mm hole size exact, 4.1mm Clearance fit, tapping size= size-pitch(generally) 4-0.7=3.3mm=taping size (depends what % thread form you want, but this easy calculation is good enough for 99% of usage).

Imperial=the same in principle but it's more awkward to work out (without a calculator) what say 40TPI is as an actual pitch size and then subtract that from the number drill size then work out what the closest imperial size drill is for that, or find your tables.

 

[rharshberger]

Metric screws are readily available on ebay as kits for the same price as any imperial screw. There is no price difference if you plan ahead and are talking about having stock in place for building.
An imperial tap and drill costs the same as a metric one if you are prepared to wait for it to be delivered.
Always remember if you want it at the right price you're going to have to wait. If you want it now, you're going to pay the price.

A rocket for me is a year project. With covid, that will be a 2 year project on this cycle.

Everyone's reason to be doing this hobby is different. If you're building a rocket this weekend or coming up to a deadline, use whatever you can get hold of that works for you and you've got spares of. I doubt anyone chooses screws based on a deep rooted philosophical necessity.

Only if you deal with Ebay, personally my money goes local whenever possible, so.....locally its more expensive to buy metric why because I live in the USA where metric fasteners are not as common as they would be for you in Austrailia, I encountered the same issue trying to 3D print some really nice Fly Away Rail Guides that were made with metric shafts and fasteners...no metric shafts available locally of that size, and iirc a #4 screw and nut was a perfect replacement for a M4 machine screw and nut, all I had to locate then was 4 shafts....ended up using 4 inexpensive carbon arrow shafts and 3D printed bushings to allow their use. Availability is a very local thing unless you enjoy supporting other countries (China's) economy, but my money is used as locally as possible.

 

[OverTheTop]

Just because something is a Standard, doesn't make it standard. Try finding an M11 left hand thread nut.

17/32" isn't standard either, but I have a tap and die in that size. Non-standard is just more expensive and harder to find.

 

[rharshberger]

17/32" isn't standard either, but I have a tap and die in that size. Non-standard is just more expensive and harder to find.

That is definitely a weird size, another oddball is the thread size used for lamp barrels (all threaded tube connecting lamps and lighting fixtures), I have tap and drill for it since thats the same thread one of my reloading tools (Stoney Point O.A.L gauge) uses for its dummy casings, it was cheaper to buy a tap and drill and use brass casings I already had than buy the casings at $5 or six dollars each, it saved me a bunch of money.

 

[OzHybrid]

Only if you deal with Ebay, personally my money goes local whenever possible, so.....locally its more expensive to buy metric why because I live in the USA where metric fasteners are not as common as they would be for you in Austrailia, I encountered the same issue trying to 3D print some really nice Fly Away Rail Guides that were made with metric shafts and fasteners...no metric shafts available locally of that size, and iirc a #4 screw and nut was a perfect replacement for a M4 machine screw and nut, all I had to locate then was 4 shafts....ended up using 4 inexpensive carbon arrow shafts and 3D printed bushings to allow their use. Availability is a very local thing unless you enjoy supporting other countries (China's) economy, but my money is used as locally as possible.

I think we're moving into political pihlosophy now. Not the benefits of a screw type.

 

[OzHybrid]

USA boltdepot.com • 866-337-9888 The only bolt I can compare on a size basis is the Stainless 18/8 pan headed 5/16x1"Long and M8x1.25 x25 Long
There's a 1c difference. And yes the metric is more expensive. You were right.......
But wait I cant find my tables. Does anyone know the tapping size for a 5/16 x 18tpi or a M8x1.25(and it says that size in the bolt description) a 6.75, maybe a 6.7 or 6.8 or a 7 if I'm really in a hurry and it's not critical. or a 17/64 after I googled it and found the right conversion chart.
The lookup cost at least 1c in time.

 

[OverTheTop]

If you really want the size of the drill for those taps I can look it up in the Machinery Handbook. It has all the dimensions and requirements, including for all the weird and esoteric threads. No internet needed .

I asked the local bolt expert here in Melbourne about the 17/32" about 30 years ago. There was an old guy, would have been in his 80's, said he remembered that size being used around about WW2 but hadn't seen it since.

 

[OzHybrid]

Yes but as I use metric, I don't need to take my 24th edition of Mach HB with me. Unless I need to hurt someone. What is it 3000 pages. I forget so long since I had to blow the dust off it.
I too have a wide range of stuff. Including a custom made glow plug tap. Cost me $50 in 92. Ah the summer of 92.....
But I wouldn't recomend glow plug threads as a basis for a rocketry fastner system. Hmm a steam punk rocket fastned together with used glow plugs. No No no stop it....

 

[Hobie1dog]

the rocket I'm starting has all SAE fasteners in it.

 

[Greg Furtman]

A bigger argument I have (between Canada & the US) is:
Robertson vs. Phillips screws. Much more of a mish-mash in [our] daily life

I don't like Phillips when compared to square (Robertson) or star (Torx) screws. No camming out. And I hate slotted screws. I own 2 VWs and everything is metric. Lots of hex caphead bolts and Triple Square bolts.

 

[Greg Furtman]

A few years ago a pen pal from German (like me he's an amateur telescope maker) visited me when he came to the States for a business conference. I took him into a local L&M Fleet Supply store which has a great selection of SAE & Metric bolts, screws, etc. When he saw all the stainless steel SAE machine screws & nuts he went nuts. He can't get SAE in Germany without high shipping costs. So he bought some of everything of all sizes. I bet he bought 3 pounds of small SAE fasteners.

 

[JoePfeiffer]

The only thing worse than Phillips is slotted. Naturally those are the only options for just about any screws at the hardware store...

 

[Jay Rairigh]

I made a hatch door for the Orion spacecraft. All dimensions were in inches.
We are not flying to Mars on the metric system.

 

[Alan15578]

I don't like Phillips when compared to square (Robertson) or star (Torx) screws. No camming out. And I hate slotted screws. I own 2 VWs and everything is metric. Lots of hex caphead bolts and Triple Square bolts.

I have not had occasion to take any tool to my VW yet. I think you meant hex head cap screws (bolts). I have no idea what Triple Square bolts are. Where are they on a VW? Or, is that just a manfacturers brand name?

 

[0011001100]

I have not had occasion to take any tool to my VW yet. I think you meant hex head cap screws (bolts). I have no idea what Triple Square bolts are. Where are they on a VW? Or, is that just a manfacturers brand name?

12 pointed bolt basically

 

[Greg Furtman]

I have not had occasion to take any tool to my VW yet. I think you meant hex head cap screws (bolts). I have no idea what Triple Square bolts are. Where are they on a VW? Or, is that just a manfacturers brand name?

Triple square are also known as XZN. Imagine taking a square drive & rotating it 3 times, 30 degrees each time. You end up with 12 points. On my 2000 & 2005 Golfs they are used to attach the drive shafts to the transmission and a few other places.