rjtedge

Hi all,

I just beginning on my framebuilding journey and have what is likely a very stupid question. When I am about to but my tubes to size ready to mitre how do I know how far to cut - for instance is my top tube is to be 58cm center-to-center how do I know where to put my mitre? I know I could get a rough idea by munising the radius of my head tube and seat tube, but this does not seem very exact.

Suggestions welcome!

Cheers

BenCooper

You really need to work out a few more numbers, as it also depends on the angle between the tubes of course. How are you designing your frame? If it's on layout paper, you can just draw the tubes on the paper and measure. If it's in BikeCAD or similar, the software can give mitre-to-mitre distances.

Other things to remember:

If it's butted tubing, then you're only meant to cut one end - ends are marked.
Mark the tube so you know which is the top and which is the bottom, so the mitres align.
Cut a little long, and gradually file away until it fits.

Mark Kelly 

The answer is contained in the question. For the top tube to be 580mm C to C it must be 580 - (HT diameter*cos HTA + ST diameter*cos STA)/2 between the top centres of the mitres. If you don't like maths, use one of the available programs like "tube notcher" which will calculate the offset for you.

Brian25

when Ben says cut off one side of a butted tube, he is strictly referring to the seat tube. (Typically butted for about 150 mm or six inches, so the front derailleur does not squish the seat tube.) Most top and down tubes have thicker butting sections on both sides, and if you were to cut off all on one side you will end up with an end with no thicker butting. (thinner & weaker) up against the bottom bracket and seat tube. Personally, I use a hole saw for aluminum frames I build, and for small production steel I have been happy with using a bench grinder for mitering. Also it should be noted that a disc, or abrasive saw is right for cutting steel , since you would need a hack saw blade with about 90 teeth per inch as to not rip all the teeth off. good luck brian

unterhausen

if I understand you right, that is not correct. There is a long butted side and a short butted side on all butted tubes that I'm familiar with. Lots of people using hacksaws on steel with success.

MassiveD

I do it in CAD. just regular CAD. Say one has a seatube of 1.125" Top tube, and Head tune. Both the verticals are 73 degrees say. I have different tube shapes pre-drawn, and I just drag them in and rotate them into position. But some people just have some rulers that are tube sized, or use drawing instruments. One the tubes are drawn in their actual position, you can see the points of overlap. So take the top of the tube say it is 560 mm long with the cuts. you cut one end to 73 degrees, now go back along the top 560, cut the second miter. The only odd bit is that you are measuring to the bottom of the notch. The actual piece will be longer overall, but how much depends on the thickness of the intersecting tubes, and the angles, etc... But it's easy, you just take the measurements off a drawing, and cut to the bottom of the notch,

It really helps to get past the BS stage as soon as possible, and measure your parts for your drawing from actual purchased parts. Then just start drawing, it will come together, and your questions will be answered from the plan. By get by the BS I mean that it helps to have the actuall BB, they aren't all the same size, the drops, real wheels that will be used. It isn't absolutely essential, but a lot of problems are easily solved with the real numbers.

BenCooper

Yes, butted tubes have a long butt and a short butt - you cut the end with the long butt. Otherwise you'd have no idea where the butt was.

Hacksaws are fine for cutting tubes - and I mitre with hole saws.

fietsbob

Sharp half round files work fine to shape the miter .

rjtedge

Hi All,

Thanks for the help, i'll use a program to get the sizes right and check it against an actual drawing!

Cheers

Rob

ksisler

OP; I will avoid saying "Google" or U-Tube or RTFM...

However the info you request is rather readiliy available in any frame building book, class, related site or design tool, as well as on most any site for companies that sell tubing notchers on Amazon, etc.

To get you started today, recommend go to the top of the framebuilders forum that you posted in and find the thread for the framebuilding suppliers. Click on Nova Cycles and look along their lower left menu. You'll find this link:

https://www.cycle-frames.com/bicycle-...e-Notcher.html

Hope that helps get you started.
/K

PS: edited to apologize... I was in a foul mood when I posted. Now am all [

ksisler

UMan, Brian25 -

Getting to the basic principle being danced around;

A double butted tube generally has a long butt and a short butt, although a good number of tubes are seen to have the butt the same length on both ends especially in short/small tubesets. A tube should be marked to identify the short butt end (=don't cut me), but some brands are marked for the long end (= do cut me). Important to know the OEM producers
data sheets and read the order page and take good notes.

However I have on several occasions received a shipment with a few odd tubes mixed into say an order of 10 each Columbus downtubes. I try to always check each tube to locate the start of the taper on each end and then draw a line around the outside of the tube with permanent sharpe pen at the right spot. There are fancy tools for that but a decent caliper can be found. I just took took a pair of 3/16 inch SS rods, sharpened a point on one end and then bent the sharp end to 90 degree about 1/2 inch in. This gives two nice feelers. Then use a rubber band around the other end of them and slip in a piece of small rod or tubing about 3/4 inch diameter of so at the end of the rods. It is then easy to slide one point down the inside of the tube and the other goes down the outside. Siding the tool in and out one will see the rods move when they slip from the thicker butt down to the thinner taper. Put a mark there. Repeat the other end and mark it.

If one end's butt is shorter, make your first miter there without cutting the length down... I think that is the gist of it.

/K

JohnDThompson 

As long as you know the center-to-center distance, you can do this without either a full-scale drawing or fancy mathematics. First, miter the short-butt end of the tube to fit. Rough-cut the long-butt end to be somewhat longer than the final length. Then dry-fit the tubes into the lugs. Use a metal straight-edge to scribe a centerline on each of the intersecting tubes:



Use the straightedge to extend the centerlines to the point where they intersect:



Repeat on the other end:



Measure between the two intersection points and adjust the insertion depth until you get the required length between intersections. Use the inside of the lug as a template to scribe the final cut at the proper distance:



File the miter to meet your scribed line.

Mark Kelly 

The lengths people will go to to avoid a simple bit of maths.....

JohnDThompson 

Hey, it was easier than breaking out the slide rule to do the maths...

Andrew R Stewart 

John- That slide rule would make a neat tie tack... Andy.

Mark Kelly 

Wow, that thing looks like it's a metre long. I guess you can fit more numbers on that way.

BTW you and I are possibly the only people on BF who can still use a slide rule. Hell, I'm old enough to remember log tables: as in literally remember the numbers and use them for doing things like molecular sulphur calculations.

JohnDThompson 

More like a couple meters long. It's an "instructional" slide rule that was destined for the scrap bin from my wife's employer (public high school) that she salvaged for me. But I do have more than a few other slide rules that I've accumulated over the years. I remember when my college Chemistry prof bought a high-tech electronic calculator with *four* functions *and* memory while the rest of us were still using slide rules...

unterhausen

I have a slide rule, but I never bothered to learn to use it. Probably one of the nicer slide rules ever made, just obsolete and I bought it on a clearance table at an office supply store. I remember them spending a really long time teaching us logarithms in high school, but never used them enough to remember any values. I refuse to do calculations in my head, a man has to know his limitations.

ksisler

OP: Now that I am in blissful happy and helpful mood; Try this to extend the answers

https://www.syncnotcher.com/calc/index.html

Just plug in the numbers and it does most of the work ... as this is demoware only, look for free stuff on uTube, etc., that does similar functions. If looking for technique, the Medford site has a free pdf file re tube notching 101 that covers a lot of helpful ground.

If shopping for tools recommend this one in particular: https://medfordtools.com/notchmaster.html Post or PM if have questions or need a startup shopping list (not to say that one can't do a great frame with little more than a hack saw and a file as I did many that way. Tools just speed up the effort and add some precision.

/K

TiHabanero

Don't make mountains out of mole hills. For my first frame I did it exactly like JohnDThompson and it was precise. Second frame I did the same way. Third frame, well, you know the story. Yes, this winter I will do it the same way...again.

MassiveD

On the BS thing, there is a perfectly reasonable discussion of butts up there, and you do have to have some minimal clue, or a competent supplier, before you order. But once you have the tubes, you can just measure the butts. You don't really need any fancy equipment to do it. So rather than a million posts and opinions, make a drawing, use real parts for your info, and you will find it all falls in place.

Andrew R Stewart 

This is exactly what i do. Measure where the butts are (butt i do use a fancy tool), line the tube up on my plans WRT the butts then cut and miter to fit. If you've taken the care to get tubes with well arranged butts you'll have no problem mitering within the thicker ends. However when making an odd frame, like the S&S coupled one I've just started up, some playing is needed. Live using an OS top tube for the DT. Andy.

BenCooper

With S&S frames, I usually find it a lot simpler to make the frame, then cut it in half to fit the couplings. That way it's easier get everything to line up.

Andrew R Stewart 

Ben- yes, I've been suggested to do the couplers after the frame is built. But I made my first one placing the couplers in the tubes first and that worked well enough for me to do again. If I did this often i'm sure i would try your way at some point. Andy.