Stagger toothed S&F milling cutter regrind

Any one had the pleasure of regirinding a stagger toothed S&F milling cutter where the stagers have a very slight helix angle - each alternate tooth has the helx angle reversed? I have a Clarkson T&G so I should be able to accomodate the angles required (I hope!)

It apprears the primary clearance is insufficient at present, the tools is dragging at the bottom of the slot it is cutting and the primary land is showing this.

I can post a picture which may help in understanding my problem.

View of the cutter showing the reversed 'helix' on alternate teeth. 15 x 2 teeth on the cutter. Note the lack of primary clearance where the cutter is rubbing in the bottom of the slot it is forming. Cutter is 3/16" wide x 3" dia x 1" bore.

I am completely self - taught with milling and sharpening the cutters, so I certainly don't know it all. Never tried to sharpen a cutter like it. At a guess, I would think that cutter and grinder need to be set up to sharpen alternate teeth, all at the same helix angle. Then a change over to the other helix, again grinding alternate teeth. I think that after grinding a tooth, the cutter would have to be moved to one side then shifted round to the next tooth to be ground then back to the original alignment. A sort of 'ducking' alternate teeth.

John

Thanks DMB for your thoughts.

Your description matches what I was considering. I think I need a small cup wheel and set the cutter up with the 'nose' down at the helix angle and then traverse the cutter across the cup. after sharpening 15 of the teeth I can then turn the cutter around on itself and repeat for the alternate teeth.

I'll give it a go and report back!

Martin

I would agree with DMB using a similar method used on circular saws which also have staggered alternate teeth. The simplest way would be to sharped-n the alternate teeth and then turn the cutter around on the spindle before re-aligning and cutting the other teeth. A proper tool sharpener probably simply changes its angle before lining up with the second set of teeth.

When I learned cutter grinding during my apprenticeship, we used Jones & Shipman and Clarkson cutter grinders.

The work is held on a tapered mandrel, and the spring-loaded 'finger' (usually made from a piece of hacksaw blade) rests against the face of the tooth being cut. In this video, the operator uses the finger against a a different tooth of matching hand.

Sharpening a side and face cutter.

This was deprecated where I worked, as there can be slight variations in the position of the flutes or gashes, especially some reamers which are deliberately milled with flutes separated by slightly different angles to minimise the risk of chatter.

Bill

As above I would index off the tooth being ground, I believe my Clarkson cutter grinder manual shows this? i will see if I can find it.

Tony

OM - Yes I go along with that, by swoping the cutter around I should get the identical angle for second set of helical teeth. The Clarkson can cater for the helix angle with no problem.

BD2 - That is a good video on the basics. I've previously sharpened similar cutters to that in the video with no problems; its the catering for the helix that caused me to hesitate and ask for any advice that others may have been here and done it. My Clarkson has a range of spindle detents formed on the rear retainer ring for varying numbers of teeth but as you say some cutters have non uniform teeth for chatter prevention and to stop tri-lobing of reamed holes where 6 teeth can create a problem. I've never seen the page, shown in the video, with the information chart for cutter wheel size vs grindstone diameter and off sets to apply for land and angle. Does anyone have a scan of that page by any chance??

TP1 - I have the ability to index off the cutter teeth, or as mentioned previously, off the cutter arbor spindle retaining ring. the tooth stagger does look even though.

Thanks all for your inputs

Martin

Martin, you beat me to it ! I think you need the Clarkson book ! If you send me a PM with Email I will send it to you. Noel

This (and the next page) may point you in the right direction:-

**LINK**

Oily, a slightly more subtle point should be made - the part of the wheel that's cutting should be in line (say, vertically, for most setups) with the finger. These are generally rounded, so if not aligned properly, the cutter will rotate a bit too much as the flute comes off the finger. We generally used cup wheels, where this is slightly easier to acheive, and dressed (carborundum stick) the inside of the wheel to leave a narrow edge that contacted the work.

Grinding wheels were often dressed to become quite narrow, disc wheels were dressed almost to a feather edge for grinding the cutting faces of small hobs (gear cutters). Similar to side and face, slot cutters and the like. The front face (of the flute) is ground to preserve the (rack tooth) form of the hob, any formed milling cutters (radius, angle, vee, etc) would be ground the same way.

Bill