I was asked if I could sharpen a 2 3/4" diameter, 1" bored cutter on the Hercus T and C. I was provided with a couple of photos that showed a cutter in a pretty sad state so I thought well, if I'm not drowning I'm well and truly way out of my depth. I have never sharpened a milling cutter.
The cutter appeared to have rust in its gullets which would make the smooth traversing of the cutter over the grinder's tooth support finger probably an impossibility. Turned out that the "rust" was caked on dirt after a thorough scrub with a brass bristled brush in a bath of kerosene. I was told that a flap wheel had been let loose in the bore to remove some corrosion. The bore showed signs of slight galling.
With the cutter cleaned I checked its fit on some 1" PG 4140. It wobbled. Then I tried it on the 13's pristine horizontal milling arbor. It wobbled. There has to be some clearance to enable the cutter to slide on but this seemed excessive. My initial thought was to use my short 30 taper saw arbor with the drawbar end held in a 4 jaw mounted on the workhead and the outer end of the arbor supported by the tailstock's dead centre. With the excessive play this wouldn't work so a mandrel would be required. The exact diameter(s) of the mandrel was going to be a challenge as was the measuring of the cutter's bore. I have telescopic gauges and an internal mic but I struggled. Alan "C-47" rescued me when he loaned me his Etalon Ingage, a direct reading internal micrometer. A number of readings around the bore at one end showed a variation from 1.0013" to 1.0017" and the other end of the bore, 1.0029" to 1.0031". What my measuring didn't reveal was that the smaller bore was tapered by about half a tenth.
The mandrel had to be made between centres because of the endless test fitting and I did resort to fine wet and dry backed onto a flat file to remove the required whiskers. But I got there. Some may question the out of round bores and their fit on a reasonably round mandrel but the bottom line is that if I do manage to sharpen the cutter a purpose made arbor would be required to support it. And probably 4 to 5 horsepower to use the thing according to Alan. My 2 horsepower mill wouldn't have sufficient puff.
So now I'm at the point of setting the cutter up on the grinder. Clarkson provided a chart of heights of the wheel above the centreline of the cutter to obtain the correct sharpening angles. I think I need to make up a centre height gauge to facilitate the alignment of the spindle and the centres on the table. Once I've sorted the height thing out can any experienced T and C hand or hands proffer any useful tips? I don't have another similar cutter to practice on.
BT
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The cutter appeared to have rust in its gullets which would make the smooth traversing of the cutter over the grinder's tooth support finger probably an impossibility. Turned out that the "rust" was caked on dirt after a thorough scrub with a brass bristled brush in a bath of kerosene. I was told that a flap wheel had been let loose in the bore to remove some corrosion. The bore showed signs of slight galling.
With the cutter cleaned I checked its fit on some 1" PG 4140. It wobbled. Then I tried it on the 13's pristine horizontal milling arbor. It wobbled. There has to be some clearance to enable the cutter to slide on but this seemed excessive. My initial thought was to use my short 30 taper saw arbor with the drawbar end held in a 4 jaw mounted on the workhead and the outer end of the arbor supported by the tailstock's dead centre. With the excessive play this wouldn't work so a mandrel would be required. The exact diameter(s) of the mandrel was going to be a challenge as was the measuring of the cutter's bore. I have telescopic gauges and an internal mic but I struggled. Alan "C-47" rescued me when he loaned me his Etalon Ingage, a direct reading internal micrometer. A number of readings around the bore at one end showed a variation from 1.0013" to 1.0017" and the other end of the bore, 1.0029" to 1.0031". What my measuring didn't reveal was that the smaller bore was tapered by about half a tenth.
The mandrel had to be made between centres because of the endless test fitting and I did resort to fine wet and dry backed onto a flat file to remove the required whiskers. But I got there. Some may question the out of round bores and their fit on a reasonably round mandrel but the bottom line is that if I do manage to sharpen the cutter a purpose made arbor would be required to support it. And probably 4 to 5 horsepower to use the thing according to Alan. My 2 horsepower mill wouldn't have sufficient puff.
So now I'm at the point of setting the cutter up on the grinder. Clarkson provided a chart of heights of the wheel above the centreline of the cutter to obtain the correct sharpening angles. I think I need to make up a centre height gauge to facilitate the alignment of the spindle and the centres on the table. Once I've sorted the height thing out can any experienced T and C hand or hands proffer any useful tips? I don't have another similar cutter to practice on.
BT
Attached Images
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Read the full thread at metalworkforums.com...
Helical Plain Milling Cutter Sharpening - A Challenge
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