Bull Nose Live Center

[Ray C]

I'm told there are three kinds of lathe operators, those that use toolpost grinders, those that do it begrudgingly and those that simply won't allow it. Right now, I'm somewhere between "begrudgingly and won't allow it". That said, I'm pulling the tool grinder out of storage. I've been meaning to build a table for this device for a while now and it will be placed next to the other grinders, belt sanders, sandblasting boxes etc.

So, here's the old beast that still runs very tight. From the picture, you can probably see how this will pan-out. It might take me a day or two to get to this so hang in there.




Later...

Ray C.

 

[Silverbullet]

Nice grinder, really I'd have some jigs to do some sharpening on specialty cutters.

 

[Ray C]

Nice grinder, really I'd have some jigs to do some sharpening on specialty cutters.

Yes, this is a more "general purpose" cutter/grinder made by KO Lee and I've made various taper reamers for sizes that you just can't get anymore. These days, when you buy a cutter/grinder they are really designed for sharpening carbide endmills and cannot do odd-ball pieces like this one. Anyhow, yes, I've made some custom fixtures to hold pieces and make strategic grinds. It's pretty good for that.

Because of limited space, it's been in the storage room but, I recently parted ways with an old B&S surface grinder which freed-up some space for now. I am however, in the market for a new grinder but this time around, it will be a smaller one. When it comes to surface grinders, I only do small pieces and have no need to hold better than half thou. If the right SG comes along, I might part ways with the KO Lee.

BTW: That KO Lee looks small but, it is darn-toot'n heavy! It is very thick cast iron.


Regards

Ray C.

 

[Ray C]

Sorry, but there aren't too many action shots of grinding the nose. It was a matter of setting-up indicators to set the angle then, hand turn it in the spin-indexer while slowly cranking the table. It was a slow process and took about an hour and was a two-handed operation which took a while to get the rhythm down. Could only take off roughly 1/3 thou per pass and about 20 minutes in, my arms were screaming at me. Stopping to take pictures was not in the cards.

Anyhow, as you can see, little Leila was impressed by it. I think it looks better in person than in the picture. My cheapo camera flares-out when it gets a strong reflection.



I have not put it on the granite table of truth but, the angle is looking pretty nice. That measuring scale (LOL: I call it the Angle-ometer) measures angles with surprising accuracy. It's made by GemRed (some off brand) and it reads dead-on with all the precision squares and angle blocks in the shop. It also re-zeros with surprising predictability. So, just holding by hand with a light behind it, I'm consistently getting an angle of 30 to 30.1 degrees. So far, so good... The real truth will be told when the mating part is finished and we find-out if the whole darn thing wobbles or runs true. -Keeping the fingers crossed...



Ok, next we're going to start on the MT3 holder part. Can't promise how quickly we'll get that done because (I'm sure you noticed) it's darn cold and it's costing real money to heat the shop. Hopefully, we'll make a little progress this weekend.

Regards

Ray C.

 

[Ray C]

Now we're working on the non-spinny piece by cleaning it up and cutting it straight. It bowed a little bit during the heat treating. In this first picture here, I've already flipped it once to catch the other side. It would be best to spin between centers but, with enough care the part can be setup in a chuck and held with a tailstock without making barrel (convex) contours in it. (NOTE: Last sentence edited to correct descriptions about concave/convex).



This piece is hard (RC 53) so I use a little cutoff-blade to dig a starting point for the tooling. Notice the paper towels to catch (most of) the grinding dust. I sprayed the paper towels with kool mist to grab the dust better. There's plenty of meat to work with and once I get down another 40-50 thou, the hardness will ease-up. There are reference materials which show hardness vs distance from the surface. It drops off rather quickly.



Cleaning up the angles and back-side. The sharp angle is purely aesthetic.


Here's the overall setup.


Next steps are to get the OD of the big part to size then, turn the entire thin part of the shaft to the largest diameter that it needs to be. That will allow me to hold it in a 5C collet so I can start boring-out the body. Once that is done, I'll flip it around, indicate it very carefully and cut the MT3 taper.

We're getting there...

Regards

Ray C.

 

[Ray C]

Didn't have much time to mess with this because I'm doing other things in the shop (like weekly cleaning and maint).

Here's how far we got. The body OD is turned to size and the front was faced off. A very straight 1/2" hole was bored to the necessary depth and the first step for the oil seal was taken to depth but stopped 75 thou short of the final ID. If folks are interested, I can describe how I sneak up on the final cut and usually nail it on (or within) the forgiving side of 1 thou. Also, when drilling hardened metal, I do a series of chasing bigger holes after smaller ones going about 1/2" depth each time. Typically I use a 1/4" dia pilot drill for 1/2" depth then chase it with a 1/2" bit.

Anyhow, the metal here is wonderfully hard. At this depth in, I'll guess about RC 35. To me, that's ideal. I much prefer working on moderately hardened metal.


Here's what we're making BTW.


OK, that's it for today. Probably a little more coming tomorrow.

Regards

Ray C.

 

[ddickey]

I'd like to know Ray. I'm sure others would too.

 

[tertiaryjim]

Nice work! You must have a very solid lathe to get such fine finishes even machining hard steel.
I wanted to chime in about heating bearings for fits just because so many people unfamiliar with it will be following
your post.
Most small bearings, like your using for this project, have interference of only 2 tenths and those bearings designed for it
may have more but thats unusual for small bore bearings.
If the bearing has dust covers or seals it can stand much less heat and if the cage is brass or plastic that will also limit
how hot it can be.
My calculations show that heating the bearing to 300deg F. would give 0.002" expansion of a 1" ID race.
0.0000067 X 300deg F. X 1"
I would think that 200deg F. would be plenty hot and allow plenty of time to transfer the bearing to the shaft with
a 0.0007" interference.

 

[Ray C]

OK then... I toss those questions out because I have no idea if anybody is watching this or not. I'm not doing this cause I need the practice... LOL...

I'll write it up and post either later tonight or tomorrow AM.


Ray

 

[Ray C]

Nice work! You must have a very solid lathe to get such fine finishes even machining hard steel.
I wanted to chime in about heating bearings for fits just because so many people unfamiliar with it will be following
your post.
Most small bearings, like your using for this project, have interference of only 2 tenths and those bearings designed for it
may have more but thats unusual for small bore bearings.
If the bearing has dust covers or seals it can stand much less heat and if the cage is brass or plastic that will also limit
how hot it can be.
My calculations show that heating the bearing to 300deg F. would give 0.002" expansion of a 1" ID race.
0.0000067 X 300deg F. X 1"
I would think that 200deg F. would be plenty hot and allow plenty of time to transfer the bearing to the shaft with
a 0.0007" interference.

The lathe is just a Precision Matthews 1236 -about 8 years old now. It's fine for stuff like this. Just need to use the right inserts, nail the F&S on the money and get the approach angles just right.

Yep... you gotta watch the temps with bearings. Good bearings will have spec info available from the manufacturer. The low-end bearings are more of a concern but, in the absence of synthetic seals, 325 (even 350) is safe territory. Tempering really won't start happening until 375-400 and it would need to be sustained for over 30 minutes. At those lower temperatures, maritinizing is more of a time-game.

Ray C.