I’m certainly no machinist, but I was thinking a carbide tipped hole saw might be worth a look.
I have used them with more favorable results than the carbon steel version.
It obviously requires the ability to adapt to your setup.
I’m sure someone has 1-3/4” but the arbor might be the challenge.
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I don't think you are going to have good luck with a 4 tpi carbide hole saw in a notcher set to cut or notch an acute angle. Perhaps not enough teeth engagement to cut accurately on such a guided cut at an angle to the work. Something tells me you need more teeth in the cut than fewer with either bimetal or carbide. But try one and find out. Hole saws really need a pilot to help pull and guide them--try one in your drill press attempting to do a straight hole where all the teeth are engaged--no 1/4" pilot not the best choice. You can see the wobble well at even low speeds. Notcher's suffer from what you are showing here by using a hole saw as a machine cutter in another application from what it is designed for. I don't know of anyone using them--I use a pipemaster layout transfer one with pins or the Zaktamark one with plastic fingers to make the pattern on the pipe or tube set in position and marked with a soap stone. Then it can be removed and burn them to the profile. if you don't have a oxy-acetylene set up--I have used a sawsall to rough the profile and finish with a grinder. I never spend more than 15 minutes doing one this way on 2 NPS or 10NPS that I am saddling.
I use Rotobroaches to 3 1/4". I have a 1 3/4" one it is XL200 1 3/4". they work good in a radial arm drill press or mag base drill but their down fall is they shatter with not a whole lot of lateral loading. Attempting to use them other than perpendicular might be an expensive experiment. It did not work for me taking the head off a Bridgeport mill and attempting to drill holes on the inside of a cylinder for a boiler drum with that head attached to a homemade supporting device. The 3 1/4" one I used doing some drilling in 1 1/4" carbon steel plate straight through--was blowing one up about every 7 hours at about a grand a piece. One they dull--more downward pressure is the downfall for shattering.Valid points.
From what I have read, and Youtube videos, most roll cages notchers use a holesaw bit. The guys who build roll cages for a living use a mill type machine with an annular cutter for notching..
I'm researching "rotabroach cutters" 1-3/4" bit. I just don't know if they make, or can be adapted, to be used on a tube notcher like I have.
Annular bits.....
https://hougen.com/cutters/rotabroach-advantage.html
I use Rotobroaches to 3 1/4". I have a 1 3/4" one it is XL200 1 3/4". they work good in a radial arm drill press or mag base drill but their down fall is they shatter with not a whole lot of lateral loading. Attempting to use them other than perpendicular might be an expensive experiment. It did not work for me taking the head off a Bridgeport mill and attempting to drill holes on the inside of a cylinder for a boiler drum with that head attached to a homemade supporting device. The 3 1/4" one I used doing some drilling in 1 1/4" carbon steel plate straight through--was blowing one up about every 7 hours at about a grand a piece. One they dull--more downward pressure is the downfall for shattering.
BLU-MOL brand hole saws are what brand I use now and have better life and cutting with them--you might give them a try. I found I have one of these 1 3/4" ones marked Bimetal and 45mm. It has about 8tpi. No part number on it.
Would this be helpful?
There is another option…..but it’s primitive.Making a paper pattern to be used for marking a straight line the length of a tube is useful information. Definitely need that for clocking purposes. Machine cutting notches is going to be the most accurate way imho vs hand notching. Notching accuracy is kind of critical for a roll cage. After the Barracuda is completed, I'll be starting on the 1968 Dodge Dart. That's going to be a full 12 point cage. Lots of tubes to notch so using a tube notcher will be easier than hand notching, imho. I purchased a tube notcher now so I could work the bugs out of it and fine tune it if needed, which mine did.
The expensive tool is going to be the tube bender. I can't believe how much vendors are asking for the them, well into the thousands, and that's for a manual hand operated bender. I'm currently looking at a Vevor tube bender because it comes with three radius dies for $600 dollars. I'll upgrade the Vevor bender with a Swag hydraulic kit so no manual hand bending. This should keep the cost just under $1,000.
My only other option for the 68 Dart is to purchase a prefabbed cage, they're around $800-$1,000 for a 12 point cage. I just don't know how well they fit, so I'm at the mercy of their fabrication design.
There is another option…..but it’s primitive.
I did some stuff for a guy with a 56 truck that’s one off…nothing manufactured.
I’m sure you are familiar with packing a tube with sand to prevent it from collapsing when bending.
It takes a little to make the radius die …but the die , a rosebud, and a welder is all that’s required.
I’d really enjoy access to a mandrel type bending machine, but it’s a lot to invest for so little use in my low budget world.
Welding…..it’s like dancing with your sister.
Looks like something is going on….but there’s nothing to it