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  #1486  
Old 01-16-2020, 08:49 PM
bob heinatz bob heinatz is offline
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I am sure Dave would love to build you something nice.
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  #1487  
Old 01-21-2020, 11:22 AM
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sparky33 sparky33 is offline
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How do you achieve tight miters with complex joints when cutting the tubes with hand saws? It seems impossible to do reliably. How do you lay out the correct line and angle for cutting? How do you ensure a perfect cut?
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  #1488  
Old 01-21-2020, 11:48 AM
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MattTuck MattTuck is offline
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That brazing is probably the nicest ever featured on a roll bar.
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  #1489  
Old 01-21-2020, 08:27 PM
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pdmtong pdmtong is online now
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A roll bar is not a DK bike.

It doesn't need to be aligned perfectly.
The weld doesn't need to be pretty.
The tubes don't need to be spec'd to the rider.
The geo doesn't need to have mm precision.

We need to educate your car friend on the the mad metal skills you employ to imagine and then execute your bike metal work!

That said, who else has a fillet roll bar? c'mon this is over the top great. and yes, just because you can, you should.
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  #1490  
Old 01-21-2020, 08:39 PM
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David Kirk David Kirk is offline
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Quote:
Originally Posted by sparky33 View Post
How do you achieve tight miters with complex joints when cutting the tubes with hand saws? It seems impossible to do reliably. How do you lay out the correct line and angle for cutting? How do you ensure a perfect cut?
Like any other skill it seems impossible at first and takes lots of time and in the end doesn't come out that great....but in time it gets faster and more accurate once you learn the tricks...or in my case make up the tricks and perfect them.

One beautiful thing is that when two cylinders (tubes) intersect the lines where they meet end up being straight lines. It seems crazy but that's how it works. So one can use a hacksaw and make straight cuts at the proper angles and you are most of the way there. Then it's a matter fine tuning the fit and angle of the miter by hand.

Complex miters like what you show are slightly more complicated but not that big a deal. Miter the bottom of the seat tube and get it just right and set it aside. Then do the same with the down tube. The miter where those two tubes interest is also a straight line and if you look at the photo you linked you can see that it's straight. The trick is knowing where to make that straight cut.

I do not use paper templates but I hear they can work OK. I don't use a computer in any way. I use a flat surface, a machinist square, a straight edge, a hack saw and various sizes of 1/2 round files. A simple miter like a seat tube-to-bottom bracket will take just a few minutes to get dialed in. A complex one like the down tube and seat tube meeting will take about 5 minutes.

I could save a little bit of time using a vertical mill but not enough to justify the purchase of the mill and the square footage needed to keep this thing that I would use only a few minutes a week. So I hand miter stuff instead. Focusing on hand skills and not tools is what allows me to work from home in a very small but otherwise free space.

I don't mean to sound flip about this at all. It's not easy to do. It took me many years to figure out a pattern so I can do it quick and very accurate...frankly tighter than a machine miter will give in most cases. But it can be done....in fact I do it this way on every frame I build and have for the last 17 years.

dave
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  #1491  
Old 01-22-2020, 01:19 PM
82Picchio 82Picchio is offline
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Quote:
Originally Posted by bob heinatz View Post
I am sure Dave would love to build you something nice.
Hi did. I was dumb enough to sell it..............
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