View Full Version : "Facing a groove"?...

12-29-2006, 11:26 PM
Lets say i have a piece of two inch solid round and i want to cut a 1/4" wide 1/4" deep groove on the face of the 2" round. (in other words there would be a 1/4" groove around a 1" diameter hub and then a 1/4" thick ring on the outside).

How do i go about making this groove in the face of the material? I can't figure out how to work around the chatter and the ugly marks it leaves behind. I guess i could grind a sharp point on a cutter and use that to cut my groove...just re-sharpen alot

I don't know how clear that was...i hope you all can follow me... :D

So what do i do / how do i do it??

12-29-2006, 11:41 PM
More info would be good, like what material, how long the part is, how you're holding it, and how large a lathe you're using.

If it's 2" stock, unless you've got a pretty sizeable spindle bore or the part is short, there will be a lot hanging outboard of the chuck. Cutting a groove such as you describe can be pretty chatter intensive with anything less than a rigid setup, so minimizing the length outboard is important. Can you center drill the work and support it with a live center?

Once the setup is as solid as possible, grind a tool thats quite narrow and has some relief on the sides, Almost like a parting tool. Lock every axis you're not using, and rough in the grove.

I usually use a very small brazed carbide boring bar to finish the feature.

It's also possible to trepan a grove such as this.

12-29-2006, 11:48 PM
Only use a tool bit an 1/8" wide, with just a little top rake and cutting oil, center the toolbit in the middle of the intended groove, feed in the 1/4", then widen the groove on either side to the required dia.

If you still get chatter your gibs are loose or the lathe is worn a bit, then you can turn your tool bit up side down and cut with the chuck in reverse, be sure to set cutting tip on center. If you lathe has a thread on chuck, then you can't cut in reverse, but ,move your tool bit past center on the other side of center and with the bit still upside down cut the groove in foreward/normal chuck rotation.

Your tool bit will lift a bit removing all excess play in the gibs and cut without chattering, and the tool bit won't dig in, it will lift away from the work. I have cut out 1" thick pipe flanges from plate steel this way using the above methods.

12-30-2006, 08:41 AM
Unless you've got an incredibly robust and massive lathe, you'll never do it all in one cut. As others have said, use a narrow toolbit and do it in stages. Try an 1/8" wide cutoff tool; if it still chatters, go down to 1/16" wide. Once you get it roughed out, you can do a "dusting" pass across the bottom to even things up.

Paul Alciatore
12-30-2006, 12:48 PM
I suspect that your problem may be clearance on the tool. The side clearance angles needed will be altered by the curvature of the sides of the groove. Thus, the inside side will not need much clearance or perhaps even a zero clearance angle as the curvature of the 1" diameter it is cutting will provide the needed clearance.

However, the clearance angle of the outside edge of the tool (that cuts the 1.5" diameter) will need to be increased or a secondary clearance will need to be cut in the lower half or 2/3s to account for the curvature.

I did a quick sketch of your tool and groove. If the face of the tool is 1/8" wide and 1/4" high, the outer edge of the tool will need at least a 9.8 degree clearance angle. If you are using 5/16" or 3/8" tools, an even greater angle will be needed or the height will need to be reduced to 1/4" for the portion that enters the groove.

I did some parts with a similar but larger groove. I actually made three tools for the job. The first had a 45 degree tip and was used to cut into the stock near the outer edge to within a couple hundreths of the final depth. The second had a 75 degree tip in the opposite side and was used to rough out the inner edge and bottom. The final tool had a flat tip about 1/8" wide and some side clearance (as viewed from above) on each side. It had the extra clearance (viewed from the front) needed for the curvature of the groove's sides (the first tool also had this added clearance). I did the final cut in two passes, noting the dial settings on the first and then measuring the results. I made the necessary adjustmentw to each setting on the final pass to allow machinning all three surfaces in one pass (in, across the bottom, and out).

12-30-2006, 02:04 PM
Dunno if this helps any, but I needed to cut O-ring grooves in a face. Old machinist mate put me onto the trick, easier to do than describe. Grind a broken centre drill as a trepanning tool.
Rgds, Lin

12-30-2006, 06:38 PM
Thanks guys! Got alot to think about here...

The piece is only protrudes from the 3-jaw chuck about 1" so i haven't had any problems there. I started off trying a 1/4" by 1/4" bit - cut fine for about 1/16" of an inch. Then i decided that was way to big so i went to the smallest piece i had lying around. I used a 1/8" by 1/8" HSS bit. It cut an additional .110" fine but everything after that was horrible chatter. I'll check all of my gibs again (this is on a 1 yr old Smithy 3-in-1 deal so i don't think its worn...just small and loose) and then i'll grind some side relief on the cutter (this is my first time playing with HSS so i dont really know what i'm doing...i keep opening up the machiniery's handbook to look it up but i get distracted reading other interesting sections :D )

After that i might try cutting in reverse and see what happens. Thanks again guys!