View Full Version : In the groove

11-04-2005, 11:52 PM
I have a disk of aluminum that I turned to a diameter of 4.5", then I faced it .300" thick. I want to turn a groove about a quarter of an inch from the outer edge. The groove will be 0.150" deep X .5 inches wide. Specifically it will be wide enough for the head of a 5/16 bold to just fit in. I will be drilling bolt holes every 60° in the center of this groove. The bold heads will sit down in this groove so that they do not turn. You get the picture. What is the best practice for producing this groove? Should I use a cutoff blade and plunge it in lightly and then move it from side to side? Should I make a custom bit from HSS and how would it be shaped different than a cutoff blade? What is the best practice, procedure and bit type for doing this type of plunge cutting? Thanks in advance for your input. I tried doing this procedure by mounting the disk on my rotary table in my small mill but I have too much slack in my table and the chatter was too much and the finish was not good.

11-05-2005, 12:59 AM
I think the cutoff tool will drag to much on the curved surface, and it's likely to chatter from the side loading.

With a depth of 0.150 and a width of 0.500, you've got plenty of room for one of these triangular carbide bits to work a little more than halfway across.
Use the one on the left to do the inside half of the groove, and the next one to do the outside half. Or, just swing the toolholder. By measuring off the face after you change tools, you'll be able to get the bottom of the groove flat.


[This message has been edited by winchman (edited 11-05-2005).]

11-05-2005, 07:21 AM
Personally, I'd grind a HSS toolbit. Just relieve the "outside" side of the toolbit so it doesn't rub where the side of the slot you're cutting curves under it.

11-05-2005, 07:50 AM
Why not just counterbore the bolt holes?

[This message has been edited by PBMW (edited 11-05-2005).]

John Stevenson
11-05-2005, 08:20 AM
<font face="Verdana, Arial" size="2">Originally posted by PBMW:
Why not just counterbore the bolt holes?

[This message has been edited by PBMW (edited 11-05-2005).]</font>

Because the bolt head would still be able to turn.
Jim wants the annular groove so that the inner and outer diameters will fit two opposing hexagons on the bolt head.
Just like the circular tee slot on a lot of lathe top slide fastenings.

A parting tool will do this fine but you may have to grind a relief at the lower portion of the blade to prevent rubbing.
The shallower the tool the better as regards interferance.

Sir John

11-05-2005, 08:58 AM
Ahhhh...I see
Well, Continuing to think outside the box, what about a set of 1/2 in wide slots made with an endmill?

Lew Hartswick
11-05-2005, 10:27 AM
If available, do it on a rotary table on a
milling mach. Do the holes next without
changing setup, automatically centers the

11-05-2005, 10:50 AM
I just had occasion to do something similar, albeit on a smaller scale, for a
valve for a rotary steam engine.

Using a sixty degree insert tool, I roughed out the groove, removing most of
the material in the 'middle' of the groove but leaving, of course, thirty
degree sloped sides. I cleaned up the outside 'side' of the groove with a tiny
boring bar narrower than the groove width. For the inside 'side', I used the
same boring bar but running the lathe in reverse. Worked very well and left a
nice groove with sides perpendicular to the bottom.

Regards, Marv

Home Shop Freeware - Tools for People Who Build Things

11-05-2005, 11:44 AM
like SGW says grind the right tool for the job. Like any tool just think out where you need the clearance and it becomes easy to grind esp with a .500 wide groove. piece of cake. This is the right tool for the job, in terms of finish, speed, setup etc. the clearance is all wrong, esp on the OD side of the groove, for inserts.

11-05-2005, 01:55 PM
Seems like a good place to use a round HSS bit.

11-05-2005, 02:26 PM
I would end mill it using a rotary table of some kind, or for the lathe I would grind a custom hss bit with relief angles to suit.(unless you have suitable cutters, as in the pic above) If I were doing it on my smaller lathe, I would use a 1/4 wide hss bit and hollow the end portion somewhat so I wouldn't have the full width trying to cut at once. Moving the cutter forward and backward will get you the flat bottom for the groove, and with less chance of chatter.

I find the worst part of grinding the relief angles is the outer side, which unless you round it under will rub on the groove you're making. You just have to pay attention to the minimum diameter of circular groove you can cut with the shape of your side relief. This only applies to the outside cutting edge.

George Barnes
11-05-2005, 03:05 PM
If the only purpose of the groove is to capture the head of the bolts and prevent their turning, this might be a little easier solution . Drill the holes and then use a 1/2" end mill and cut a slot that is .150" deep for .156" each way from the center of the hole. As far as that goes, the slot could be 90 degrees to what is shown if that would have any advantage for the application.


Just another idea.

11-05-2005, 04:24 PM
Looks nice George, and leaves the disc a little stronger.

Paul Alciatore
11-05-2005, 06:37 PM
I had to cut a similar groove a while ago. I used a series of three tools which I ground with 1/4" tool bits. I first applied some blue and made light circle marks with a sharp pointed tool near the ID and OD of the slot.

The first tool had a straight edge on the left side and a 45 deg edge on the front/right. The left side was relieved to allow for the outer edge of the slot and the front/right 45 deg edge was relieved for cutting by plunging straight in or cutting sideways. I started the cut with it a little bit inside the outer edge of the slot and plunged in about 30 or 40 thousanths per pass. Then I cut toward the inside of the slot until the 45 deg edge was just a bit from the inside edge. I continued with additional passes until I was about 25 thousanths short of full depth.

The second tool was a standard right (left? I always confuse them) hand cutting tool. It has about an 80 deg angle at the tip and is ground in a standard manner. It was used to clean up the 45 deg inside edge of the groove to within about 10 or 15 thousanths of the final diameter. Again, about 30 or 40 thousanths deep per pass.

The final tool I used was a slightly modified cutoff tool. It is about 1/8" wide at the tip and slightly less behind it for clearance. It has clearance on both sides and the front for cutting in all three directions. I also added a slight radius on the two corners for fillets but that is optional. I ground additional clearance under the left edge to clear the OD radius of the slot. I touched the ID of the slot and the face of the disk for reference and then cut about 5 thousanths off the ID, botton, and OD while noting the dial readings for each cut. I retracted the tool and measured all surfaces. With a little math, I had the dial readings for the finished size. A second pass, starting at the ID again and going actross the botton and out the OD had the slot pretty close to final size. I went by the dial readings I had calculated. One final measure and cut cycle and it was done.

I was nervous about this cut but with a bit of planning it was done with no problems. Just plan ahead and all will be right.

Paul A.

11-05-2005, 07:11 PM
Thanks for the replies. I did the small dia ones on the rotary table and they came out all right, but the larger one did not work too well due to the fact that I have too much back lash in my small 4" rotary table. Actually the bash lash is very very minimal but enough to not give a good finish (As seen now mounted on my lathe). The x y axis is locked on my mill to preserve the bolt hole dia so it matches its counter part precisely.

11-05-2005, 07:13 PM
Where did the pictures go? Give me a minute to figure out how to post a picture.

11-05-2005, 07:37 PM


11-05-2005, 07:51 PM
This too cool. this could make me dangerous.

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