PDA

View Full Version : parting tools -- hss (need help)



Tony
11-06-2002, 01:10 PM
i bought a stock piece of HSS ...
its about 8" long x 1" tall...
the crossection is a tapered rectangle
(ie trapezoid).. 1/8" at the "bottom".. thicker at the top.

i've shaped it and reshaped and just can't seem to get good cuts... lots of chatter, not very clean cuts, my parting tool moves, too..
it cuts a slight cone instead of a clean face.

i've ground about a 15 deg relief on the face of the tool.. and a "lead-in" both positive and negative (ie tried both directions) and i've also tried grinding it square (the the length)

any recommendations?
it seems to cut better with lube but i'm just throwing coolant away by the gallon. i've seen this done dry.

i'm not cutting any exotic metals, by the way.. mostly mildsteel and SS occasionally.

kap pullen
11-06-2002, 01:41 PM
knuckle,

how are you holding it?
You need some kind of a solid mount either bought or homemade to hold it vertical and straight.
You need a gentil "lip" on top to give you side clearance in the slot.

5* to10* clearance on the front and on center, supported with minimal overhang and she should cut.

Not enough feed will cause chatter and wear.

Too much can cause a bind up and crunch.

It's a fine line there.

Keep the slot clear and coolant to the cutting edge all the time.

On a deep cutoff, I'll go in say 1/8", pull out move over 1/16" and cut to 1/8" below the first cut and repeat this procedure till done.

Wear youre safety glasses!

Good luck.

kap

Dr. Rob
11-06-2002, 01:51 PM
Hmm, yeah...I used to experience nastiness like that until I realized the most deciding factor was rigidity.
The parting tool and the job need to be set down rock-solid. Bolt it down, screw it down, clamp it down into a heavy, rock-solid holder with rock-solid mounts into a rock-solid toolpost on a rock-solid cross slide and lock the carriage down too.

Surprisingly, feed rate is often just a little more than what you'd normally dare. Don't be chicken; FEED it rather than letting it rub a little.

Coolant/lubricant? Yup. Keeps the swarf rolling off the top of the tool, among other things.

Judging by the angles you've mentioned, it seems you know what the tool is supposed to look like.

Low RPM's too, by the way. And practice on spare chunks to save yourself the grief when it doesn't work as I say.

Rob Frink
11-06-2002, 06:58 PM
Knucklehead,

Here are a few rules of thumb that I use:

1.)To reduce chatter, raise the tool untill the chatter goes away. The higher the tool, the less the work piece will try to "roll" over the top. You'll find a "sweet spot" where the tool cuts nicely....and if you go any higher, the tool will just rub without cutting. You'll know it when you find it.


2.) On the top of the tool, grind a "cup" lengthwise along the top edge. This cup causes the chip to fold-up edge to edge which makes it narrower that the kerf...hence easier chip removal.

3.) Use a flood coolant/lub and go slow and hand feed. Speed up as you get a feel for everything.

4.) Everything needs to be rigid! Cut as close to the chuck as you can, extend only as much parting tool as you need.

Good luck,
Rob

Rustybolt
11-06-2002, 07:03 PM
If you have a rear toolpost put the tool in upside down. This helps top keep the chips clear which is the biggest cause of tool breakage. Make sure you onle expose enough blade to do the job and be sure the tool is really sharp a dull tool will grab the work and snap.Good advice all.

Thrud
11-07-2002, 12:56 AM
knucklehead:
My dad used to call me knucklehead...no, it was numbnuts. I never knew why either...oh yeah, blasting caps and 1/2 sticks! Oh, to be young and stupid again...

You are cutting a cone section because the tool is not perpindicular to the work. I do this deliberatly with plastics to make dished washers. Make sure that the tool tip is dead on center height and use adequate cutting fluid or lots of coolant. The swarf should come off like a tiny roll of toilet paper.

I suggest you may want to make sure that the tool is tight and secured to the tool post as it sounds like it could be moving under power. Make sure your cut-off blade holder secures the blade - it should never move in the holder! Keep the blade overhang to a minimum for maximum ridgidity.

kap pullen
11-07-2002, 07:13 AM
Thrud,
We used to get what we called Hammerheads.
Farmers used them for bird control.
We'd launch can heads and do general distruction that would quickly put a child in jail, or theropy these days.
My big brother lost the end of his finger in some experement.
They grafted skin off his posterior to repair it.
To this day, I don't like to shake his hand.
Still have all my digits. Just lucky I guess.
kap

Thrud
11-08-2002, 02:53 AM
Kap
Strangely enough, fire crackers were impossible to get when I was a kid. Caps, sticks, and fuse was another matter. That I just walked into the hardware store (in town) and they went int back got what I wanted. http://bbs.homeshopmachinist.net//biggrin.gif

My unle lost all but his thumb and little finger on his right hand. He was out chopping wood with his brother and he dared him to chop them off - then he placed them on a stump. So he did. When is mother run him to the doctor the Doctor asked for the fingers, so his brother took the horses back and found the cat just finishing off the last tender morsel. http://bbs.homeshopmachinist.net//eek.gif

He was pretty good with that little finger and thumb though (fifty+ years of practice will do that...) - he could open a book of matches and rip one off and light it all with the two digits.

lynnl
11-08-2002, 11:05 AM
C'mon Thrud, that's not REALLY a true story about your Uncle? .. is it?

Thrud
11-09-2002, 04:06 AM
lynnl:
Yes it is true. Every time his little brother argued with him after that he would hold his hand up in his face and say "Remember this? That's what I thought." (end of arguement)

True story.

There was a bounty on gopher tails of .05/each in 1917 here in Alberta and my Dad would catch the gophers, cut the tail off and let them go - "So they can grow back and we can re-catch them!" (I am not making this up)

Moral: Make your children go to school!

happy02
11-09-2002, 08:52 PM
Are you using a rocker tool post? If you are then you can get more regidity by not using the rocker. In other words use washers to shim the tool holder so the tool is at the proper height. Also run the lathe very slow; backgear if its a bench model. Minimum overhang for the tool and the tool bit should enter the word at 90 deg.

milmat1
11-16-2002, 04:36 PM
One of my fondest memories of childhood. We had moved into a big farmhouse on ten acres, well there were a great many large old growth trees on the place, My dad(god bless him) Would use dynamite to remove these giant stumps. We would drill all around the stump and place the sticks in the holes and blow them to smitherines! He would let me touch the wires to the battery on the tractor to set off the charges SHEEEW!!!
He once had the bright idea to lay an old mattress over the stump to keep the flying dirt down, Well at the end of the driveway that mattress stayed in the top of an old oak tree until it rotted and fell down hahaha......
He used to tell us that playing with firecrackers was dangerous. and dynamite was much more reliable !!!!

kgarver
11-18-2002, 07:39 PM
When I was kid we lived on a farm in southern Indiana and we had a 3 acre field that had a small stream runniig across it at a 45* angle. We damed up the stream and rerouted it to flow down the fence line to the river. We had extra top soil to fill in the stream bed but the tree stumps had to go. Dad and I went into town, on Saturday morning, walkeded into the local hardware store, Birches, and said "give us a box of of dynamite please". They said "regular or extra strength". Not knowing anything about dynamite Dad said, "Extra strength". They also sold us prima cord and threw in the blasting caps for free! They put the prima cord and blasting caps in a brown paper bag and the two boxes of dynamite they carried out to the car and put them in our trunk. Wish I could remember the price! (1954) They did tell us to keep the blasting caps seperate from the dynamite until we were going to use it though!
We drove the tractor to the lower field and Dad walked up to a stump , about 30" in diameter, and drilled five holes around it and put in TWO EXTRA STRENGTH sticks in each hole. He lit the prima cord and we ran back to get under the tractor about 75 yds. away.
Well, when the dynamite went off that stump tore up out of the ground in four main pieces (found three of them later about 100 yds. away) to about 250' high! The stones came down on us like a hard rain. Dented the Allis-Chalmers fuel tank something fierce! We could hear them bouncing off of the tractor tires and the seat! One broke the tail light and one whacked the tool box lid so hard that it broke free on the rebound and we never did find it. They hit the ground and glanced off of the other rocks and tree trunks we'd cut down and shot all over the place. One about the size of a baseball rolled in under the tractor and when I picked it up it was still hot. Dad said, "I think I used a little too much".
Being all of 6 years old at the time I just naturally agreed with him. Over a period of two week he gradudally refined his technique and by the time the job was done we could both eyeball a stump and tell how many holes and how much dynamite to use. When it was fired the stump just sorta jumped 6" and when you walked up to it the dynamite had just blown the dirt down and away from the roots and it was just sitting over the hole! Of course we had about a 1/3 box of dynamite left at the end of the job and we just stored it in the woodshed. Dad kept the blasting caps down in the barn in the medicine cabinet we used to store the bag balm and other medicine used for the dairy cows!
Yes indeed, it was a simpler time then!
Regards, Ken

spope14
11-18-2002, 08:22 PM
If you have an Aloris tool post, get the aloris cutoff tool holder. It has a built in rake angle on it. I use these often, and they work.

When setting up a cutoff tool, be sure to put only about 1/8 inch more cutoff tool out of the holder than you need, rigidity.

Also, be sure the tool is as straight and square to the work as you can get it - I indicate mine, I am too careful, but break them very seldomly. I also gring a 20 degree angle at the point, the point facing the "off end" to get the best cut. leaves a better face finish, and very little nub on the "off end".

Oil the living heck out of the cut while doing so, and if you feel comfortable, use power feed. I use about .001 feed rate. Using power feed keeps consistant pressure on the cut, and prevents binding...check your compound rest backlash before hand to be he right way. Power feed also prevents "jumping" into the cut - gouging it and breaking the tool or creating the dreaded chatter that these tools are known for.

Set the tool at center for 1 inch or less, .010 above center over 1 inch - flex (from a text book, it works).

Watch your tool in the holder to be sure it does not start to "skew", or move off to the side or off square, a common problem. I find the angle on the tip helps this.

Never hold work on the off end with a live or any center.

All of the comments above come from 16 years of teaching using these tools, and getting over a hatred of the tool to finding at least a very good comfort with them. Seen a lot of broken tools in the first 6 years, only three the last ten.

I know this thread has been on the page for about a month now, but I had a hard time getting to it and finding my notes.