Surface finish from Chipmaster

[charadamParticipant @charadam]

[charadamParticipant @charadam]

I have spent a very frustrating day in the workshop.

My 1974 Chipmaster has always given me acceptable to very good results depending basically on the material being turned. Its original 3-phase motor is inverter driven.

On checking for taper, I measured less than .0015" over a 6" length of freecutting MS 1.75" dia, not supported at the tailstock, using a .005" cut and .003"/rev feed. The tool was an HSS knife tool.

As the narrow part of the test bar was getting close to the measuring surfaces, I decided to take .020" or so off.

With a brazed carbide tool and a .010" cut at about 400 rev/min I was rewarded with a ploughed field of the herringbone persuasion.

Checked everything – gibs, slideway oil, chuck cleanliness and tightness, toolpost tightness, tool height etc.

Tried an HSS tool and slower speed – very slightly better but not acceptable.

Tried an insert tool and approx 800 rev/min and the finish was acceptable.

My preference however is to use HSS tools and low speeds/feeds.

Any suggestions gratefully received.

[AjohnwParticipant @ajohnw51620]

Try taking a cut of about 0.040" deep with a decent hss tool with a very small rad and a feed of say 0.002" or more per rev and see if it's better. Probably headstock bearings if it is – especially of increasing the feed rate also helps.

Also check that the tools aren't over centre by taking a facing cut. A tiny touch, thou's under doesn't matter much. A touch over centre on a braised tip carbide tool is very likely to matter as the clearance angles will be low. Also any tool that has low clearance angles.

John

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Edited By Ajohnw on 03/12/2016 19:14:14

[Neil WyattModerator @neilwyatt]

I'm guessing that you have been using the machine for along time and you know what tools/feeds & speed suit it and this is not usual.

Do the spindle bearings need nipping up? Is the bar really freecutting or is memory playing tricks?

Neil

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