Feeds/Speeds/Tool Geometry with fast feeds

Used powerfeeds on my Keighley for the first time.

The "sliding feeds" as mentioned on the change gear plate are

21 cuts per inch

42 CPI

84 CPI

84CPI being equal to 0.302 mm/rev

On a big 7.5kw colchester I had gotten used to using ~0.15 mm/rev using quality carbide tooling for roughing.

When I tried 84 CPI (20-80-100 gears with intermediate (80) being randomly selected) anything but a tiny depth of cut at 600RPM in 25mm steel would jam in and stall the lathe.

The coarse feed of 21 CPI is starting to go into thread cutting range.

I'm guessing there is a hole in my knowledge because I can see no way any of these feeds would be useful. Anyone please enlighten me?

Seem way too coarse to me. For finishing with HSS it's nice to be able to get down to two to four thou per rev. (that's about .05mm to .1mm). You'll need to find a way to reduce the gearing. No idea how you do that on a Keighly.

Your Keighley is essentially a Mk1 Denham Junior so the threading chart shown on the 7 th picture down here ; - **LINK** probably applies.

Looks like you need to alter the gears on the banjo. If that chart is right you have 30 - 70/80 - 90 as your drop gear train which is also the setting for 21 TPI. Probably 20 - 90/49 - 120 or 30 - 120/80 - 70 would be more appropriate for feeds giving 216, 180, 54 and 224, 112, 56 cuts per inch respectively. Translates to 4.6, 6.5, 18.5 and 4.5, 8.9 and 17.9 thou per rev. No reason to stick with the chart of course as you can manipulate gears at will.

Clive.

Looks like it works in a similar way to my Warco 280, three selectable feed rates per gear train setup. As Clive says you need to alter the gear train to something finer otherwise you are doing little more than cutting a fine thread.

At least the chinese blank out the feeds that are not really practical to use.

Edited By JasonB on 28/06/2017 12:02:33

Alas I wish I had the MK2 lathe, if anyone wants to swap I would be very happy

I will have to fool around with the train a bit, however for general reference and future keighley owners who have lost their plate here are some pics.

Or, I suppose the simple way to get the finest feed available is to put the smallest gear you have on the spindle, the largest gear you have on the leadscrew, then on the stud you put the second-largest and the second-smallest in your set..

Yeah did some maths 1:1 would be 1.51mm/rev. 20, 100, 25, 127 gears give 5:127 or about 0.06mm/rev. Will have to print off a new sheet of feeds and keep it pegged somewhere. Gonna grind up the tool from "southbend swarf" so I can rough with the same feed. Never appreciated quickchange gearboxes so much