View Full Version : HOW to? interrupted cuts on a lathe.

12-03-2004, 04:43 PM
I started out this morning with a simple job. Boring a coupling to fit the motor/gearbox I am replacing the truck transmission and motor on my shaper. (more compact) I have a free 5hp TEFC motor and truck tranny now if anyone needs it.

The coupling has three 9/16ths set screw holes in it. The first boring bar went about a inch into it, hit the first hole, started shaking at each pass of the setscrew. I backed the cut off. It still snapped. Out came boring bar #2. Same story. OUt came the home made boring bar (welded 90 degree) it went about 1/4" more then snapped.

I got one more, a carbide cut and welded 90 degrees. I know it will shatter.

I have broken everything I have touched today. Starting with a fluke 77 I have had since the 80s. I need a battery for it I think. It worked twice, been out in the cold shop. It will not ohm. (*the new shaper motor) On ohm scale it measures but in the megaohms, not going down to zero resistance when the probes are together.

I ran a piece of conduit, it wrinkled in a 90. *used conduit I told myself. I pulled wire into it anyways. (30 years in that field)

I got to go to the bathroom, but am afraid to "handle it". It might fall off.

(the motor did run without a "ka-boom" tho) I must admit I never turn things on I can't check first. I closed my eyes when I flipped the switch on. Have you ever heard a "ka-boom"? you know the split second before, the whole world goes immediately silent, you could hear a pin drop.. then KA -(bright light)Then BOOOM (loud noise).. Not a good thing for a electrician (molten copper faster than my smelter can).. I had proper grounding, right breaker in, the proper overload, and was flipping the switch standing on a piece of rubber. (after the way the day has gone) So of course it went just fine.

Ohh yeah the question was: how do you bore something with a keyway or a hole like this? I was using HSS cutters, not carbide.

I blame the day on TechTchr.. he said so.


12-03-2004, 04:46 PM
Take light cuts, I do this with a small carbide boring bar on my south bend 9".

12-03-2004, 04:54 PM

The obvious answer, and the one you probably already know, is to fill a hole with a screw and a slot or keyway with a length of steel or brass or some-such. Sometimes it works to simply fill the gap with an epoxy like JB Weld. On the other hand, sometimes nothing works and you just have one of those days.

J Tiers
12-03-2004, 05:02 PM
<font face="Verdana, Arial" size="2">Originally posted by BillH:
Take light cuts, I do this with a small carbide boring bar on my south bend 9".</font>

Or fill holes like the other post said.

Interrupted cuts let the cutter snap back as the cutting force is released. Then it smacks the work again. Light cuts do help, and they cut down on the noise.

Maybe there is some excessive looseness in the setup, like a boring bar stuck way out? That might affect matters too.

I actually have not busted anything on interrupted cuts. On other stuff, yes.

Usually the nasty noise tells you that you better not do that. But if it busts right away, there isn't any noise but the loud "snap". Don't ask how I know that...and I won't tell you how long I worked grinding that cutter........

12-03-2004, 05:18 PM
I am done for the day. Took one shot of Evan's namesake whiskey and it went down and my ears are on fire *were cold, now red.

I'll try again tomorrow eve, gotta go repay the kindness of Mikey (helped put the metal on my roof) We are pouring concrete into a footing. Hopefully. He thinks he is pouring three truckloads. (24 yards a big house) I don't think he can get concrete on Saturday.

The bike has to wait too. I gotta make spacers for the 3/4 axle & rim. I sure hope I ain't gotta bore nothing, cause I got nothing to bore with.


Alistair Hosie
12-03-2004, 05:41 PM
Sounds like you've had a bad day Dave sorry to hear it Alistair

Spin Doctor
12-03-2004, 05:57 PM
Use the absolute heaviest boring bar you can get in the hole with the absolute shortest amount of overhang. And as you did use HSS. If you don't have any heavy bars a job like this is the perfect excuse.

12-04-2004, 11:23 AM
Spin, the first one was on a 1" square shank. I had it extended 6" to reach the bottom of the coupling.

SINCE: I retrieved my loaned out port-a-band saw and will cut the coupling down. The gear box I am using has a 2"L x 1.5" shaft. I think I have over 1.75 bored out so I will cut that rascal off. If not? It would have been easier to have started with a chunk of iron. Built the whole end. I'll come up with something unique one the shaper runs back and forth.. (adjustable boring bar) I got a Old boring head I got off ebay. It won't fit the lathe tailstock.

Off, onto the roof.. up up and away.. (got a leak between the old part and new roof and it is sun shining today.


Crazy Ed
12-04-2004, 12:00 PM

(the motor did run without a "ka-boom" tho) I must admit I never turn things on I can't check first. I closed my eyes when I flipped the switch on. Have you ever heard a "ka-boom"? you know the split second before, the whole world goes immediately silent, you could hear a pin drop.. then KA -(bright light)Then BOOOM (loud noise).. Not a good thing for a electrician (molten copper faster than my smelter can).. I had proper grounding, right breaker in, the proper overload, and was flipping the switch standing on a piece of rubber. (after the way the day has gone) So of course it went just fine.

Yeah, I was lucky!! Back about 1985 or so, I was a 'U-build 'em, I burn 'em' test tech at Hornywell before it became a bunch of Bull. We had this 208v 3 phase 'ac control' test adapter box for an old resell item. We had been waiting for test equipment repair to get the box back to us. Well, they did. I hooked it up, and luckily got to horse playing around with the TER tech. The back triac heat sink just behind the fine spread metal was pointed innocently across the hall. There was this 'future customer' and our sales rep looking into the 'clean room' assembly across the hallway. I reached down almost set the circuit break on, got the sillies, and said " it is your honor to flip the switch". Well this went on for a couple minutes of 'no its yours to do' and luckily the group went around the corner. I, in final act of sillies, flipped the switch with my foot, ONE very very loud, ear ringing BOOM and orange red fire all the way across the hallway. Lights out, emergency powered lights on, blacked plexi window on clean room, tile floor black/gray later (1/4 second) I turned in shock to look at the slowly?? turning red face on the tech. I asked him why he was turning red? Seems he had wondered why the 'triplet ohm meter' was off ten minutes after he had checked to see IF the case of these triacs was isolated!!!

Luckily, the 'customer tour group' was around the corner. The 150amp circuit breaker had fused, the area 600 amp had tripped!

Boy, we were lucky that day. There would have been plenty of ambulances there had I NOT got the sillies. about 15 people in that group including some very nice looking legs sticking out of 4 dresses. I dug out a chunk of molten aluminum from that wall about 1/4 x 1/8 inch!!! And about 1/2 way thru the sheetrock!!!! Sheez!

I can only imagine what would have resulted as a result of me just flipping that switch without going thru the 'sillies'. FYI, I almost had pulled it on with the group there. I still get cold chill bumps thinking about it.

I immediately went down the hall the direction they disappeared amd made sure that they didn't come back up that hallway, but went another direction!! I found them and pulled the rep aside and told him not to and to come by later. You should have seen his look when he heard the whole story!! Funny, policy was changed, we could not power on anything that hadn't been powered on previously when any tour group was anywhere in sight!! Hehehe. Wonder why???

Whew!!!! One very close call. Some times HORSE PLAY does wonders.

12-04-2004, 12:22 PM
I have had problems while boring across internal keyways or holes. Almost always been not a rigid enough setup. After cinching everything down, including gibs, and breaking out the stiffest bar on hand that fits, the cuts are no problem.

I also had to flip the switch with eyes closed while standing on a piece of plywood.

I was rewiring my Clausing drill press to 220v. I checked and double checked everything to ground, looks good, threw the large switch/fuse combo, nothing, good, turned the drill on, nothin, crap.

Went back to the switch and checked voltage, the fuses were blown, brand new fuses, damm.

I have this problem with this sw/fuse combo, I can't get it to keep from cookin fuses.

Now yer gonna cringe, I wrap the fuses with electrically conducting tape, (aluminum foil). Alright stop cringing, the circuit is protected prior to the switch with a 50amp breaker, the sw/fuse is used only for the switch.

Still it bothers me that I keep blowin fuses ? I definitely don't have any continuity between ground and supply so I'm lost.

I could actually rip the switch out, I used to use it for a disconnect to my rotary converter but I don't need it anymore.

Well David, sorry for chewin at your thread here, I'll scoot. JRouche

12-04-2004, 04:13 PM
Lighter cuts and faster rpm.It's kinda like a woman, you have to find the magic spot and just becouse it was there last night doen't mean it will be in the same spot tonight!

12-04-2004, 04:30 PM
I should add the only reason I am using carbide is because its the only boring bar I have, haven't ground a HSS one yet.

Spin Doctor
12-04-2004, 05:46 PM
Gyps, am I to understand that you were using a 1" square tool bit as the boring bar. I've never had much luck trying to go too deep with a solid HSS bar, They might be really stiff but they don't have a heck of a lot of spring to them. Get to much load on them and they have no place to go but adios. A possible source for material to make boring bars out of might be the axles out of a RWD car or truck. Back in the day when we made rear ends in house the axle shafts where 4140 or 4340 forgings

12-04-2004, 10:27 PM
Hey gypsie, it will help if you "set the drag" on the carriage snugly. It will take out some of the jumping back and forth.

12-04-2004, 10:46 PM
Crazy Ed: Kinda like the time I ran a megger-ohm cranker into a 1000vdc cap out of a primitive inverter and was going to throw it into my partners lap while he was driving? Better sense caught up, I sparked it on the door handle and it blowed a chunk out of it. He'd have turned the truck over. Or enough stored emf would have killed him.

J: The moment you post a thread, it is not "yours" it is Village Press Forum materiel. If it is offensive to you or others it is thier responsibility to remove it.
I am not a great man, but I do stand up for what is right in my heart. I had a friend who looks in here get sick over the Slave post. He was a young german during WW2. It made me cry, or at least my eyes water up or that may be just the mediciene side effects. The war guilt must have been horrible for all the surviving People. Even the children have post tramatic stress disorder.
I am trying to adjust. I got two kinds of sleeping pills, nerve pills, thyroid pills and heart medication now. None mix too well with my favorite tranqulizer (booze).

Feel free to add, ramble, talk, speak your heart out in my posted or any other post topic here.

I am sure Neil feels the same way. As the desription says, it is "your" forum.


12-04-2004, 10:58 PM
When you lowered the voltage for the machine you doubled the current..
A motor draws for example 400 watts on 480, 400 watts on 220.. Otay ? Watts div by voltage = amps . 400/480= high voltage current and 400/220=low voltage current. Otay? Make sure you are putting in slow-blo fuses also. Starting motors blow even larger quick blow fuses. they hit 6x current on startup.

I love breakers.. ya know what I did to my mill? I put a $26.00 small sub panel on the side of the rear box, take the fuses out and put in cheap breakers for each sub circuit. The machine main turns it off. Of course it is a elaborate system. Miles of wire in that crazy machine..

Fuses wear out, just like a light bulb they are always emitting, when they burn thin enough they pop just like a light bulb.

Hope that helped just a bit.

[This message has been edited by ibewgypsie (edited 12-04-2004).]

12-04-2004, 10:59 PM
Any of you ever use a "snaggletooth"?

It's basically an end mill with one or more chipped teeth that gets ground down into a single tooth to use as a boring bar. I have done that with end mills and taps. Just too cheap to throw out a big chunk of sharpenable high speed steel.

Something else I have done on interrupted cuts is to plunge the hole with a 4 flute end mill. The three other teeth and helix angle guide the cut over the interruption and the square end tracks true because there is no side load from the interrruption. The three additional flutes also keep it from chattering in the cut.

12-04-2004, 11:09 PM
What I did with the coupling? I cut it down to 2" long like the shaft, took the other side of the coupling bolted to it, chuck that end in.. bored the other end back to the previously bored part. Simple, just required thinking from the other end.

Then chucked it in the milling machine, cut a 1/2" groove in it. Put it in the vise and filed it square. Put the coupling on the gearbox and it fit without filing the key. Must've been luck.

I got to build a mount for the gearbox, motor, redo the controls, mount the linear scale on cross travel and the ram compound, mount the axis drives, the hand manual pneumatic joystick and then debug my software. I got it figured out I think.. we'll see. I have it where I can swing the indexer from the shaper to the mill. *(gears anyone?)

I got it going together. I pulled all the opto22 boards, they are in a pile. More coming in the mail. I can't wait. I'll take pictures when it all works.