How do you bridge the Metric - US Customary Gap?

[werksmini]

Where to start? Working in shops and German cars as the foundation of my mechanical experience has made Metric the de facto system of measurement. When inches are incorporated they are done so as 25.4 mm and 31.7 5 mm. I recently started working in a proto machine shop that does everything in US Customary. This took a little white to get used to but it is consistent and easy to work within. Most materials are available solely in inches/feet from the big suppliers so this all makes sense (I quit my metric bitching the first week).

Fast forward to my question; I started building a frame jig and all of the stock available is in inches. On paper, no big deal, measure stock, convert, and work entirely in metric. The DRO's on the machine tools switch back and forth easily so where could the problem be? In reality and off the paper I have found that I am switching back and forth constantly, making conversions with most processes. For example the 8020 extrusion framing is metric 40 but all the aluminum stock is inches. I know that some of the issue is that most of the tooling is in fractions but I know that isn't everything.

The question is where do you convert to Metric, if that is in fact what you use? Does anyone just stick with inches and fractions? That sounds like pushing the problem to further down the stream as most components are metric (5.12" rear axle spacing anyone?). This is mostly a survey of the more mechanized American builders here on how they operate in a double-unit-world.

Perhaps I just need to invest in more metric tooling and quit my bellyaching.

Also, anyone in the Boston area have any scrap tubing laying around? I've got beer, a shovel, and a high5 if you might be willing to part with some

[EricKeller]

if you're making your own stuff, why not go metric? I do when it's not too inconvenient. Frame tubing isn't actually metric for the most part, although it's specced that way. Since I like measurements to be obvious round numbers, I didn't go metric on that.

[fortyfour]

8020 does make Metric extrusions, are you saying they are just rebranded U.S. Customary billed as Metric? For the record, the Metric Extrusions are what I used when building my jig and some of my tooling. An even better, more refined option is Item. I've used that as well and find it a bit more accurate. But I typically will make parts drawings in U.S. Customary Units to jive with my machines (bridgeport/lathe - no DRO), and work in decimal's to a certain specification (typically thousandths). But I will be going back and forth between metric and U.S. Customary constantly on occasion. I had to do that a bunch as well when I was a shoe designer as all of the spec. sheets and drawings had to be in Metric for the factories - it is what it is and I think through that, it's just part of my process now. I have on occasion made parts drawings in metric to change things up on my end. Drawings for overseas customers all go out the door in metric.

I think if you are building professionally, and ship globally, learn to use both U.S. Customary Units and Metric with ease and know the conversions. It's a good habit to get in to IMO.

And I agree, I wish the U.S. would just switch to Metric. It is a heck of a lot easier.

[EricKeller]

pretty sure he's talking about buying aluminum plate/bars -- can't get them in metric sizes in the U.S. I like Misumi extrusion -- it's all metric and they assign all your parts a part number so you can easily reorder.

[GEBLA]

I think the US has changed to Metric long years ago. Just nobody cares. :-)

Greetings from Metric Germany, where people working with bicycles seem to be the only people that handle the conversion with ease...:-)

Georg

[fortyfour]

For example the 8020 extrusion framing is metric 40 but all the aluminum stock is inches. I know that some of the issue is that most of the tooling is in fractions but I know that isn't everything.:

Gotcha now. (I read this as 8020's Metric 40 Extrusions were in stock inches for some reason).

For the record, I have purchased aluminum in Metric Dimensioned Stock from separate suppliers. I've never purchased aluminum stock through 8020 or Item.

[edoz]

I can mentally switch back and forth seamlessly, but I tend to stick with one or the other for certain things. My fixtures, for example, are all standard hardware, as are my machine tools.
I do the Bikecad stuff in metric, and then change to inches for the fabrication drawing.

[Eric Estlund]

Measure everything yourself in whatever unit you prefer, and stick to that.

[Andrew R Stewart]

If you're making mountain bikes you need to do all in inches.

If it's road bikes then everything has to be in metric.

Andy (who personally uses cubics) :)

[werksmini]

Thanks for all the replies. This is definitely the sense that I was trying to get.

If I were just using bought fixturing I think it would make it simple. Measure everything in Metric and go from there. When getting into fabricating stuff from " stock and tooling it gets a little more complex.

The reality looks like a lot of conversions and compartmentalizing certain projects into one or the other system of measure. Make a fixture in fractions and work from there in metric. No magic bullet here.

[VertigoCycles]

Fast forward to my question; I started building a frame jig and all of the stock available is in inches. On paper, no big deal, measure stock, convert, and work entirely in metric. The DRO's on the machine tools switch back and forth easily so where could the problem be? In reality and off the paper I have found that I am switching back and forth constantly, making conversions with most processes. For example the 8020 extrusion framing is metric 40 but all the aluminum stock is inches. I know that some of the issue is that most of the tooling is in fractions but I know that isn't everything.

You're going to have to machine the aluminum stock to make your fixtures anyway right? Buy a face mill and machine it to whichever unit of measurement suits you.

[Dallas Tex]

God, I'd wish the US would go metric. Inches are ridiculous.

[Alistair]

I was raised in the UK, so metric is natural to me, but I've taught myself machining and bike making since moving to the US, so I've become quite comfortable with inch/imperial measurements too. I can shift from one to the other without trouble, but seem to gravitate to particular measurement system for particular tasks. Truth to be told, I think I probably use the inch/imperial system more often than metric. I do find that 0.001" has more meaning to me than 0.1mm when machining, but that's probably just from working on US machines than are graduated in inches.


Alistair.