Are you using metric or SAE stuff to build rockets?

[Kelly]

As I search ebay, Amazon, etc. for small hardware & tooling that I need to build rockets, I'm starting to notice a shift: Metric stuff seems to be more readily available, and at better prices, than SAE/English/Imperial/"Freedom" or whatever you want to call the other unit system. When I look on Thingiverse for stuff to print/build, it seems as though most of the stuff is specified to be put together with metric hardware. @cwbullet is posting a build thread for a 3D printed tool that has a metric parts list.
I'm comfortable with working in either system, and it's starting to seem as though there may be advantages to moving to metric (besides the obvious 'ease of use' arguments.) But, my shop is entirely built around SAE: all my drill bits, taps/dies, measurement tools, small parts etc. Has anyone here from the US moved to all-metric for building rockets (or other hobbies) ? Why? Has it benefited you?

(Not interested in philosophical or other arguments regarding metric vs SAE, those have been hashed out ad nauseam already. Just wondering about the practical aspects of switching, especially for rocketry and other maker-type hobbies.)

 

[stantonjtroy]

SAE when I have a choice. Frequently in decimals of an inch (as opposed to fractions). Metric when I don't have a choice.

 

[heada]

Its odd. All out motors are in metric. Body tubes are mostly imperial (except that BT names....which make no sense to me at all) I've been trying to convert to metric as much as possible and its easy on LPR/MPR but HPR still ends up in imperial for some reason.

 

[catman001]

While I have not gone 100% to metric in any of my hobbies, some of them are 90-99% metric. Most of my larger woodworking tools, like the table saw, router table, thickness planer are imperial measurements. Just seems to be the way most of those items are sold. I also fly and build some of my quadcopter's or drones as most call them. Those are almost 100% metric. Why? Because most of the motors, frames and other parts come from china, which is a metric country. Most RC cars, boats and airplanes are also metric for the same reasons. Only three countries in the world use the imperial system of measurement, the US, Myanmar, and Liberia. With a total population between the three of them of about 400 million vs the 7.4 billion on the metric system most manufactures use the metric system as they can reach about 90% of the worlds population.

I was like you and had mostly SAE tools, but over time added metric as needed. I now have metric drill bits, taps and dies, wrenches, sockets, nut drivers, ball drivers and other metric tools. Just the way it is if you have many hobbies.

If I am building something from scratch I mostly use the metric system, just so easy to use.

 

[jqavins]

Partly because (as heada said) the motor sizes are metric, I do my designing mostly in metric. The smaller BT sizes correspond to motor sizes, so they're metric by force, and I prefer to stick to one system, so the whole design is metric.

Then I go to buy parts and the lengths are all in inches.

And then there are those items which are neither. Machine screws, nuts, and washers which go by number so-and-so; wood and sheet metal screws which go by number thus-and-such but not the same numbers; wires that use gauge sizes; sheet metals which use gauge thickness, but not the same gauge number as wire, and not even the same for all different metals.

So I throw up my hands and use what gets the job done. Putting a #8 screw eye into a 2 inch long 24 mm bulkhead? Whatever.

Quibble: "SAE" should not be used to refer to the inch measuring system in general. It refers to particular items that are voluntarily governed by SAE standards, like bolt heads, nuts, and the wrenches that drive them, among many other things. So wrench sets are labeled SAE or MM. But there's nothing SAE about a 12 inch long body tube.

 

[DAllen]

Am I using English or metric?

 

[JohnCoker]

Mostly SAE out of habit. At this point, metric is familiar enough that I could probably switch over without much trouble.

I noticed that 3D printing seems to have standardized on metric, and people who would use SAE for building things by hand talk in millimeters when modelling.

 

[Joshua F Thomas]

As a university student of physics, and with intention to go on and teach physics in secondary education: I use metric whenever possible. The use of metric in the sciences is nearly universal.

 

[user 30299]

I use both. Especially when I looking for the right fastener for a particular application.

 

[Kelly]

And then there are those items which are neither. Machine screws, nuts, and washers which go by number so-and-so; wood and sheet metal screws which go by number thus-and-such but not the same numbers

I'm going to disagree, partly just to be argumentative , and partly because this is really the focus of my question. A 4-40 machine screw (for example) is most definitely SAE (or whatever you want to call it) because the 40 is "threads per inch", and the nut that you would put on it has flats that are in fractional inches.

My question is mostly about hardware. Yeah, like most rocketeers I measure motor diameters in mm, body tube diameters in mm or in, body tube length in inches, thrust in newtons, etc. But when I reach for parts to build an av bay (for example) it's almost exclusively SAE stuff, because that's what my shop is built around, and that's the type of hardware that's been the easiest and cheapest to get for the majority of my lifetime. But that no longer seems to be true.

Quibble: "SAE" should not be used to refer to the inch measuring system in general.

Agreed, just using a familiar term. When I ask my son to grab a set of wrenches for me, but he doesn't know what vehicle we're working on, he'll ask "Do you want Metric, or Freedom?"

 

[heada]

I have both M2 and 2-56 nylon shear pins. I have M2/M3/M4 stand offs and screws for mounting electronics but also 6-32 and 8-32 threaded inserts/cap screws for motor retainers. I normally use either 10-20 or 1/4-20 threaded rods and nuts for av-bays Anything bigger than than M4 and I'm going with SAE since that is the cheapest hardware at my local big box store.

 

[dr wogz]

I have a mish-mash of Metric & imperial in my builds: 1/4-20 eye bolts, #6, #8, and/or #10 for smaller stuff, and metric (M3 or M4 and Gasp! M6) for electronics on AV bay sleds.. Only because that's what's available (after market) or what comes with the kit..

you pointed out the obvious: cost. and that most suppliers on those platforms are coming from overseas more & more..

Sorry, I kinda chuckle at the "freedom" classification. I guess hat's a bit of a political leaning thing? Like 'freedom fries' with your burger?





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

 

[PBic]

I use mostly SAE/Imperial in tools, hardware, and design, but have been increasingly using metric for the hardware availability reasons noted by the OP. Sometimes I’ll use metric just because I need an exercise to gain better ability to visualize metric increments. I also admit using metric as a justification for more tools, because more tools is always better.

 

[Kelly]

Sorry, I kinda chuckle at the "freedom" classification. I guess hat's a bit of a political leaning thing? Like 'freedom fries' with your burger?

Exactly; and all in fun. I'm surprised we've gotten this far into the thread without the "There's two measurement systems for rocketry: metric, and the one that put men on the moon!" comment. But, I have no interest in those arguments. I was trained to be able to use either. Which one I use for a specific task depends on which one is better at the moment.

 

[jqavins]

I'm going to disagree, partly just to be argumentative , and partly because this is really the focus of my question. A 4-40 machine screw (for example) is most definitely SAE (or whatever you want to call it) because the 40 is "threads per inch", and the nut that you would put on it has flats that are in fractional inches.

Ah yes, quite right. The thread pitch is in an explicitly imperial unit, while the diameter is some oddball size (probably defined in inches, since it's probably one of the things that is defined by an SAE standard).

But when I reach for parts to build an av bay (for example) it's almost exclusively SAE stuff, because that's what my shop is built around, and that's the type of hardware that's been the easiest and cheapest to get for the majority of my lifetime. But that no longer seems to be true.

Whatever is on hand or cheap will do. And yeah, that's usually imperial, but I've gone beyond caring. But, for the sake of all that you personally hold holy, stick with one or the other for a single build.

"The screws for the ematch wires were M4, but one of then came loose so I replaced it with a 6-32. It's all good."

When I ask my son to grab a set of wrenches for me, but he doesn't know what vehicle we're working on, he'll ask "Do you want Metric, or Freedom?"

So, you're raising your son to be a smart ass. Good choice. Well done.

 

[dhbarr]

Inevitably I choose the wrong one.

 

[prfesser]

It's kind of ironic that the aluminum tubing used to construct many 24, 29, 38, 54, 75 mm motor casings is not metric stock but SAE: 15/16, 1 1/8, 1 1/2, 2 1/8, 3". (Though some 54 mm reloadable casings today are made by turning the o.d. of 2 1/4" stock.) Neither 15/16 nor 2 1/8 is very easy to find, but the others are all stock sizes. By contrast the only size of metric tubing probably in stock at most warehouses would be 75 mm.

 

[prfesser]

I use mostly SAE/Imperial in tools, hardware, and design, but have been increasingly using metric for the hardware availability reasons noted by the OP. Sometimes I’ll use metric just because I need an exercise to gain better ability to visualize metric increments. I also admit using metric as a justification for more tools, because more tools is always better.

Agreed, he who dies with the most tools, wins.

On topic, I use SAE hardware partly because it's easier to find a variety of parts in stainless. Of course I could order them but the size of rocket I generally make will do just fine with local hardware, I don't need big, superstrong eyebolts and such for a 3" rocket.

 

[Steve Shannon]

I just use whatever fits. It doesn’t matter whether you call that body tube 100 mm or 3.9 inch as long as it holds a 98 mm motor. Every good engineer I know switches between systems without a second thought. It would be good if there were just one system, but that’s unlikely anytime soon.

 

[rharshberger]

As fasteners go SAE is way easier to get and way less expensive to purchase locally, I have Fasteners, Tacoma Screw, Ace Hardware's "Hillman Fasteners" aisles (1000's of specialty parts and fasteners, even gun screws, removeable rivets, and #0 screws etsc) all within less than 10 minutes of my home, Tacoma Screw Pasco is about 1 mile away. So I chose SAE unless Metric is called for (mainly repairing stuff).

 

[Dipstick]

Haha, it may be the Canadian in me, but my brain does them all, often intertwined. In rocksim, I love the fact that you can change units right in the component. I've laughed at myself creating a tube with a diameter in mm, length in cm or inches, depending on which tape measure was closer to me at the time. If I was forced into using only one, it would be metric...

 

[NateB]

So I throw up my hands and use what gets the job done. Putting a #8 screw eye into a 2 inch long 24 mm bulkhead? Whatever.

Same with me.

Medical work has me think with metric more than anything. My rockets and life are a mashup of both. Velocity in mph, but wind speed in knots. Distance in miles typically, but are they nautical miles or statute miles? Motor mounts are metric, Tube diameters can be in inches or millimeters. Tube length is usually in inches. Weight is in grams or pounds/ounces. It is easier for me to think of thrust as lbs of thrust and how many pounds can be safely lifted.

 

[afadeev]

Metric stuff seems to be more readily available, and at better prices, than SAE/English/Imperial/"Freedom" or whatever you want to call the other unit system. [...]
I'm comfortable with working in either system, and it's starting to seem as though there may be advantages to moving to metric (besides the obvious 'ease of use' arguments.) But, my shop is entirely built around SAE: all my drill bits, taps/dies, measurement tools, small parts etc. Has anyone here from the US moved to all-metric for building rockets (or other hobbies) ? Why? Has it benefited you?

I use the two interchangeably.
For smaller units of weight, grams (in integer form) are easier to work with than fractions of an ounce. Consequently, I use grams when weighting epoxy hardener and resin amounts.
For items that are already marked in mm (all our motors), it's just easier to search for a 29mm motor-mount-tube for a 29 mm motor, instead of looking for a 1.14173" tube or a 1 and 1/8" tube.

For larger and longer units, like airframe length and diameter, it's usually inches for me. As in I need to order another G12 32" long 3" wide fiberglass tube. How much is it by foot?
I do have a conversion XLS for BT-xx to inches & mm, and avoid relying on un-intuitive (to me) BT-xx nomenclature.

Just wondering about the practical aspects of switching, especially for rocketry and other maker-type hobbies.)

Agreed, just using a familiar term. When I ask my son to grab a set of wrenches for me, but he doesn't know what vehicle we're working on, he'll ask "Do you want Metric, or Freedom?"

Both work.
All the cars I've ever owned have had metric fasteners, and now I have $-$-$-$ worth of tools accumulated for wrenching on them. That is unlikely to change any time soon, so my next car will likely be metric as well.

For rockets, anything goes.
Supplies and vendors are relatively few and far between, so if you can't get a 2.6" tube but a 66mm is on sale, I will order metric without hesitation.
If, however, someone advertises BT-80 on sale, I would need to first go an look up what size that really is.

 

[Joshua F Thomas]

Caveat to "use whatever works": If you're going to be working with others in a team, or making stuff for sale, you'd better pick one system and stick to it.

 

[Buckeye]

If, however, someone advertises BT-80 on sale, I would need to first go an look up what size that really is.

Agreed. The BT-whatever system needs to go away for good. A pointless relic of the past.

 

[Kelly]

"The screws for the ematch wires were M4, but one of then came loose so I replaced it with a 6-32. It's all good."

Yeah, I guess that's one reason I'm hesitant to switch. My "miscellaneous hardware" box will end up being a mish-mash of metric and imperial, and I'll be constantly having to pull out calipers or something to figure what I've got, or what I need.

 

[rharshberger]

Agreed. The BT-whatever system needs to go away for good. A pointless relic of the past.

And then somebody is going to have to go back and match up the new tube diameters to 60+ years of Estes parts numbers to create things like the Body Tube and Nose Cone cross references, no thanks. It works its been in place long enough its standard in the hobby and most of us know where to look when we don't know.

 

[OverTheTop]

I made the decision to switch to metric for anything I built back in the 80's. Having said that I am quite adept at dealing with both and have a great selection of taps, dies, gauges etc to work with. I am comfortable with either but metric is preferred.

Yes, the miscellaneous screw and nut boxes have a mix of both.

 

[heada]

And then somebody is going to have to go back and match up the new tube diameters to 60+ years of Estes parts numbers to create things like the Body Tube and Nose Cone cross references, no thanks. It works its been in place long enough its standard in the hobby and most of us know where to look when we don't know.

If someone were to ask me to get them a BT60 tube, I'd give them a blank stare but if that same person asked for a 1.5 inch or 38mm tube, I could pick it out immediately.

It's time to move on. BT sizes are a pain to work with because they don't match up to anything. Tubes should be listed with OD and ID and be done with it.

 

[Kelly]

I made the decision to switch to metric for anything I built back in the 80's.

But, in Australia, that's the standard, right? So that makes it a bit easier?