Abrasive Tube Notcher

[Mael Jambou]

Hi, 

Do you use abrasive tube notcher ? 

What do you think about it? Any recommendation?

I plan to purchase an abrasive tube notching machine (for steel and stainless steel tubing). I see many advantages using this king of machine:

- only one machine to notch all the tubes

- easy to set up (and relatively fast)

- belt lifetime

Here are the "settings" I am thinking about:

- Belt 60 or 80 grit

- 2 speed motor (to avoid overheating)

- adjustable roller high (+/- 10mm) => for BB notching

- custom roller (dropout 25.3mm - seat tube 28.6mm, 29.6mm, 29.8mm, 30.00mm - head tube 31.7mm, 36mm, 46.4mm - BB 38.1mm, 51mm)

There are two points I still wonder about:

- Accuracy (with thin tube thickness)

- Vice system (even if this seems sufficient given that the notching is done by removing material and not by cutting, so we don't need to tighten the tubes with a large tightening torque)

Many thanks in advance for all your feedback !

[Mark Bulgier]

Hopefully someone who's actually done it will chime in, but I have thought about it and heard from people who have, here's what I think:

• You'll want to keep it far away from delicate precision machinery like lathe, mill, and human lungs, due to the amount of grit it throws in the air.  Ideally in another room where your gritty processes happen, or outside.
• Unless you want to design from scratch, consider starting with a 2x72 "knife maker's" belt grinder, because those are common, with lots of choices in belts and accessories.
• Get a "small wheel adapter" that has 2 deflector wheels.  Deflector wheels keep the belt coming into your small wheel and leaving your small wheel parallel, not splaying out at some vee angle.  When a miter wraps 180° around the tube, like when the notched tube and the one it fits against are the same size, you can't have any vee angle.  I may not be explaining this well, easier to see one.  I don't have a pic with 2 deflectors but here's a pic with one, and you can see where the second deflector would bolt on to make the belt wrap the full 180° around the small wheel:

• Not all belt grinders can take two accessory arms like this one can.  See that second lower place on the blue frame where an arm can go in?  That's where you'd put the arm that has the work holding device on it.  Make the work platform height adjustable, to center the tube on the belt wheel.
• 2" wide belt isn't wide enough for some of your larger tubes at a shallow miter angle, so you'll have to move the tube side-to-side while grinding.  I think that'll be doable with a deep side-to-side groove in your work-holding platform, that takes an miter angle fixture, like the fence on a tablesaw.  Set your tube holder against the fence, and then it holds that angle while you slide the tube side to side.
  
• Get steel (not rubber) small wheels so you can lathe turn them to custom diameters.  Your wheel diameter will increase by twice the belt thickness, so the diameter you turn them to will vary depending on your belt thickness in theory, but I don't know how sensitive it is.  Probably one diameter can be used with thinner or thicker belts without miter accuracy suffering too much.  Typical small wheels available for knife makers come in 1/4" increments.
• I haven't researched to see if there are other belt sizes that would be better. 3" wide would be nice, and/or longer belts.  72" is OK for length but the longer they are the longer they last.  But then you might be back to having to reinvent the wheel (make your own) instead of buying off-the-shelf knife-maker parts.  I would recommend against getting belts shorter than 72"
• Anyone here know the abrasive mitering machine made by Dennis Bushnell for R+E Cycles in Seattle?  I was fascinated by it, so damn clever, but I haven't seen it in like 20 years, not sure if they even still use it.  But I think his belt length was reeeally long, longer than 72".  He originally came up with it around 1990 to miter Aermet 100 alloy, a steel so strong and tough that cutting it with holesaws was difficult, but abrasives went right through it.  Aermet 100 alloy was later turned into Reynolds 953 (Reynolds bought the tech from Carpenter I believe).  IIRC, 953 is not quite as hard as Aermet 100, but better in some ways for bicycles.
• Brazed-carbide holesaws from Torch and File (Strawberry) are more precise than abrasives and can go through the hardest bike steels, but need a really rigid machine, like a moderately heavy mill.  Not going to work in an Ol' Joint Jigger.  I can lift my 2x72" grinder and move it around the shop by hand, with the motor and VFD attached, so the abrasive method wins on weight and portability.  A lot cheaper than a Bridgeport too.
• Oh yeah the VFD, very much recommended.  The smaller the wheel, the slower you need to spin it to avoid burning out the bearings.  VFD gives you infinitely variable speed, and allows 3-phase motors on a 110V single-phase outlet.  Cheap Chinese VFDs are available but I got a good USA-made VFD for my USA-made grinder.  Better reliability, and tech support, spare parts etc available from long-established companies that speak English and can deliver parts from a US warehouse not the slow boat from Shenzhen.  I got my (USA-made) motor used on Craigslist, which saved me a ton of $$, do-able because 3-phase motors are pretty simple and reliable, not a lot that can go wrong with them (knock wood).  Other VFDs are 240V only or have other requirements, so make sure you know what you're getting.
  

[Duane Draper]

Here’s the picture Josh posted on Mael’s FB post.  Not sure if Josh is on here.  It’s incredibly well thought out.  You can see the belts to the left and the different sized rollers on the rack above. 

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