Help with Shank for Thornton cutters with ID 3.5mm

[Voodoojar]

I've been having huge issues making my own shanks for small Thornton cutters. My new wheel cutting mill uses ER11 so I can no longer use my b8 Shank from Boley.
I've tried a few different designs on the homemade shanks. The latest I cut from carbon steel. On three I made I notice I start to get some wobble after a few hours of use. I think this is happening from the shank itself slightly bending and will need to make a thicker shank. Before I put in all the effort to make a new one or Spend a huge amount to buy LB wheel cutters on shank. I was simply wondering what other people use?

 

[Jim DuBois]

I have found it necessary to make a lot of arbors to hold cutters as well as workpieces. They generally need to be trued up from time to time and tend to be ultimately disposable. And I make them of free machining steel, and I make no efforts to harden them as if the steel would do more than case harden. I have made a couple of tool steel, but that is not necessary for what I do.

 

[Voodoojar]

These are helpful to see I've been making them with 4mm rod I try going up to 6mm. I've been trying a couple of different types of steel rod from mcmaster maybe diameter is my issue.

 

[Jim DuBois]

I am dealing with larger stuff. These are generally made of 5/8" or 3/4" rounds, and I reduce the shaft to 1/2" or 5/8" on the materials holding arbors as 1/2" is convenient for collets on all of my lathes and mills, and 5/8" is used for tower clock sized work. I look for the best rigidity I can provide while allowing enough shaft on the arbor to stay away from the milling axis etc.

 

[Jerry Kieffer]

I've been having huge issues making my own shanks for small Thornton cutters. My new wheel cutting mill uses ER11 so I can no longer use my b8 Shank from Boley.
I've tried a few different designs on the homemade shanks. The latest I cut from carbon steel. On three I made I notice I start to get some wobble after a few hours of use. I think this is happening from the shank itself slightly bending and will need to make a thicker shank. Before I put in all the effort to make a new one or Spend a huge amount to buy LB wheel cutters on shank. I was simply wondering what other people use?

Assuming that that your machining procedures are sound, Arbors are pretty basic. I am with Jim on the use of free machining steel since it will more than cover the stress of cutting teeth.

Personally, I do this type work on machine tools since I am unable to get the results I am looking for on my Geneva style Lathes and Cross slides.

The first photo shows a typical cutter arbor in the 3mm range again machined from 12L14 steel. The Arbor is .189" for use with a #48 WW collet in my small Mill. The same #48 collet used for machining the arbor in the Lathe is used to hold the arbor in the Mill for wheel and pinion cutting.
The cutter is mounted in the arbor and held in place by a cup shaped washer and 1/72 stainless allen screw. The arbor was machined with a Carboloy E-4 brazed carbide tool to a snug fit per second and third photo.

I avoid using any collets or tooling from China or India for critical work as they have not proven to be consistently capable, accurate or repeatable.

The smallest arbor I have made to hold a commercial cutter as I recall, had a 1mm shank and held a cutter with a .4mm ID per third photo since it only took a minute to machine. The .4 mounting surface was threaded and the cutter was held with a washer and nut.

Without first hand observation, we would need a step by step machining procedure to diagnose possible issues.

Jerry Kieffer

 

[wefalck]

I am wondering, whether it would be feasible to make solid arbors with the same taper as an ER-collet. You cut the taper as well as you can and in the next step you machine the seat for the cutter, while the arbor sits in the spindle you are going to use with the cutter. You also mark the relative position of the arbor in the spindle, so that you can use it always in the same position. This should reduce run-out in the cutter.

 

[Betzel]

You also mark the relative position of the arbor in the spindle, so that you can use it always in the same position.

Sage advice. I do this for everything now. Still isn't perfect every time, but it's way better. If you take a carbide scraper blade and lightly run it along the Z axis at the collet's keyed position, it seems to last and is more visible than a scratch. At least I can see it in ordinary light while turning it in my fingers...

 

[wefalck]

Indeed, this is not a ground surface of hardened material, but better than doing it randomly. On the soft arbor you can make a punch mark, as the machinists of old did. If the the spindle is hard, I would try to make a line with a carbide scraper - for better visibility fill the line with a permanent marker.

 

[Voodoojar]

Here is one of my cutters on home made shank. I bought a new set of ER11 collets and now everything is fine. I think I orginally misdiagnosed my issue and in fact it was poor quality ER11 collets on a new lathe and mill.