How can I turn a bar offset?

[PatMarlin]

I'm running .100 shy of "X" travel on my CNC for one darn part.

I have 5/8" boring bars and I'm using one for turning. I machined an offset tool holder that offset the bar and gave me my .100 but it's not solid enough. I get singing and vibration no matter what speed and feed and it's not acceptable by any means.

I have a 3/4" (dia) bar coming that uses the same insert. What I want to do is turn the shaft to 5/8" on an offset, so it will fit my tool block and give me the .100 I need.

The good news is this 3/4" bar already sets the insert tip about .062 closer, so I would only need about .040 more to go.

How would you guys do this? I was thinking using my Bridgeport with a boring head. I only need to turn down 1.5" for the tool block. I think the Bridgeport setup would work but it would be real slow going as it would be a face cut all the way down.


http://www.patmarlins.com/1noOff.jpg


http://www.patmarlins.com/2offset.jpg


http://www.patmarlins.com/3overall.jpg

[Cactus Farmer]

How about a four jaw chuck on a manual lathe and off set it 0.025. That should give you a total of 0.050. I might do the whole 0.050 and gain a little extra clearance.

[garandsrus]

PatMarlin,

Are you sure your cutter is sharp?

John

[frankenfab]

What Cactus Farmer said. If you don't have 4-jaw, you can make a larger offset holder similar to what you made already, with the shank sticking through (the part of it you want reduced and offset.), then you can turn it in a 3 jaw. We had some shafts with offset crank pins we made where I used to work. That's how we did it. Kinda chattery with the interrupted cut and all, till you get down to the end of the cut.

[scb]

I'm not really sure where the problem is so this my well be a really dumb suggestion. Can you turn the boring bar over (so the insert is facing down) and cut on the other side of the hole. Instead of the side furthest from you (if the pic's are taken from the operators position) cut on the side closest to you.

[PatMarlin]

PatMarlin,

Are you sure your cutter is sharp?

John

Oh yea- new carbide CM1 insert. It is sharp. Rigidity is my problem. I didn't think about the 4 jaw chuck. Hmmm, I didn't even know you could do that.

I can't move the bar- No room. The pace between the 90drg Iscar parting tool and thread bar normally has a drill sitting there so that space is taken as well.

[JIMinPHX]

Well, the first thing that I would look at is your actual physical travel limit on your X. Most NC machines come out of the factory with a little fluff room between where the safety limit switch trips & the actual physical limit of travel. I've found that I can usually squeeze at least an extra 1/8" of travel out of most axis that I have worked on.

If you need to cut an offset on your lathe & you don't have a 4-jaw independent chuck, then you can try chucking your stock in a standard 3-jaw universal chuck with a shim under 1 jaw. That should throw it off center far enough to do what you want to do. Some guys also take a small independent chuck without a backing plate & grab it inside their universal chuck for quick little jobs like that.

You may also consider constructing a more beefy gang tool holder. I know that looks like a hefty chuck of steel that you have there, but you may be surprised to see what doubling its size does for eliminating chatter on the outer tools.

Also, constructing the block so that it will accept a boring bar extension without a reduced shank will probably make a BIG difference. You are several diameters out there with that bar now. Any time you go past 5 or 6 diameters with a steel bar, you are tempting the chatter gods. You can sometimes get to 8 or even 10 diameters with a solid carbide bar, but I've seldom had any luck doing that with a steel bar, even in a rigid machine that was cutting friendly material. If you leave your boring bar extension about 3 times the diameter of the bar itself all the way back inside the tool holder block, you should see a substantial improvement.

Snugging up your gibbs may help a little, but it looks more likely to me that you need more tool rigidity.

[PatMarlin]

I've got a 4 jaw chuck. How to you set it up to do an offset?

[John Taylor]

Use a dial indicator with your 4 jaw to get the amount of off set you need. If you are having a problem with chatter you probably have to much radius on the cutter. I do a lot of turning on barrel and grind my carbide inserts so there is no radius. In most cases it will take the chatter out.

[JIMinPHX]

Is it a 4-jaw independent or a 4-jaw universal?

On an independent, each jaw moves separately & you can set your work piece as far off center as you want. If you put your chuck key into a socket & only one jaw moves when you turn the key, then it's an independent.

If it is a universal, then all 4 jaws move at the same time & you cant really make an accurate offset adjustment, but you could still offset the work with a shim, like I suggested on the 3-jaw before.

If you don't mind being a little crude about the amount of offset, you could also take your 3-jaw chuck, open it until one of the jaws comes out of mesh with the scroll, then put the jaw back in, 1 tooth out of place on the scroll.

[JIMinPHX]

I see that you have triangle inserts with a screw hole in the middle of them. It's not all that hard to cut a tool holder pocket to accept that particular insert. You might also consider making your own custom insert tool that bolts up rigid to your existing tool holder.

[PatMarlin]

It's a 4 jaw independant.

I would like to make my own tool blocks, but right now just don't have the time. The Omni-turn blocks are pretty flimsy. I used that stainless steel in the pic to tie the parting tool holder, and the other end of the tool block into the turret.

An item I have to deal with is simply the limitations of the machine. This a turret, and the turret would normally index, but this model is notorius for have indexing problems so it's been disabled, and I have to use the gang tool type setup. I think my gibs could use some adjustment as well.

I will eventually convert this machine over to a true gang tool mounting system which will give me plenty of solid X travel and mounting surface.

But for now I have the machine performing very well for all of my dies and this one .100 tool offset is the very final detail I need to work out.

[JIMinPHX]

If you have an independent 4-jaw, then just mount a dial indicator on the cross slide, touch off to the work piece & adjust the jaws until you get the offset that you want.

If it were me, I'd blow the hole in the tool holder out to 3/4" & run that bar straight. The last thing that you want for rigidity is to have the mounting area of the tool to be the flimsy part. You can always run a smaller bar (5/8", 1/2", etc) in a 3/4" OD split bushing. Those things hold solid as a rock.

If you are going to permanently abandon the turret function & stay with only gang tooling full time, then you might want to put a pattern of dowel pin holes in the mounting surface. That will allow you to have multiple tool gangs that you can change in about 2 minutes & still have good accuracy/repeatability immediately after a tool gang change by using the tool offset function on the machine.

[PatMarlin]

If it were me, I'd blow the hole in the tool holder out to 3/4" & run that bar straight. The last thing that you want for rigidity is to have the mounting area of the tool to be the flimsy part. You can always run a smaller bar (5/8", 1/2", etc) in a 3/4" OD split bushing. Those things hold solid as a rock.




Problem is boring the tool holder, and running the bar straight will still be shy .040, and boring the tool holder out more will even make it weaker. This is an Omniturn 8 position block with 5/8" holes on 1.1 centers. It is strong if it is supported. Hanging out off the base with no support represents a problem specially with so many holes and set screw holes.

It's solid now the way I have it reinforced. I think turning the bar offset so the outer side is flush all the way down, but 5/8" in diameter to fit the holder will be the most rigid I could hope for in attempting this.

The bar's about $30 so it's no great loss, and can be used elsewhere.

Here's how I would like to turn it:

http://www.patmarlins.com/Bar.jpg

[PatMarlin]

Here's kinda what the end view would look like (1/8" offset):

http://www.patmarlins.com/BARend.jpg


I don't know if I'm wasting my time here, but if this doesn't work, then I'll have to make a tool holder with a notch to hold the insert. I'm tired of dealing with this kind of stuff. This is all I've been doing for over a year... jumping hurdle after hurdle with modifying machines, tooling and production setups...:roll:

[PatMarlin]

How would you cut a "V" notch for the insert bit Jim?

[JIMinPHX]

I'm tired of dealing with this kind of stuff. This is all I've been doing for over a year... jumping hurdle after hurdle with modifying machines, tooling and production setups...:roll:

Welcome to life as a machinist.[smilie=s:

Machining is really a thinking man's game. It's kind of like playing chess. You really need to plan your moves carefully. You've often got to estimate the time it would take to manufacture various time saving fixtures & then guess how often you would use them to figure if they are worth making or not. Often, at the end of a few years, your collection of jigs & tooling will be worth more than your machine(s).

Patience is a virtue & for a machinist, it's an especially useful one. There's always more than 1 way to skin a cat. Sometimes it takes a while to come up with the best way.

[JIMinPHX]

How would you cut a "V" notch for the insert bit Jim?

That depends. What kind of tooling do you have for your vertical mill? Do you have a turntable? A super spacer?, A dividing head? A vice on a rotating base? A sine bar? Digital Read Outs? A 1/16" reamer & some 1/16" dowel pins?

If you have a CNC mill, then it's easy. If you're working on a manual mill, then you need to pull a few little tricks from up your sleeve & extra tooling gives you a few more options to play with. It's been a while, but I've cut triangle insert pockets on a manual Bridgeport before & I've done CNMG & trigon pockets on an NC machine.

Even with limited tooling, you can make up a few small pieces of flat bar with an angle that matches the side profile of the insert & locate the small flat bars with small dowel pins on a flat surface of the tool you are making. If you have some way of accurately angling your vice, then you may be able to cut the pocket directly into the tool you are making.

A really quick & dirty way to do it would be to just use 6 dowel pins to locate the insert directly & then hold it down with the center screw. If you take very gentle cuts, you can get away with that, but the second you put a little pressure on the insert, it will chip at the pin locations & shift. You can make this slightly less bad by adding a little potting compound (like cerrosafe) to spread out the pin load. I really don't recommend the quick & dirty method though.

[JIMinPHX]

You might consider a basic tool holder design like the one in the drawing below. It could be made out of a piece of 1" (or larger) square stock. You could either turn down a 5/8" round shank for a short distance at the right end to locate it, or you could bore a 5/8" hole & press a sleeve into it. You would then hold it in the 5/8" bore on your existing gang rack with a 3/8" bolt (& a big washer) from the back. Sucking the tool up against the face of the gang holder like that will give you a wider bearing surface & much better rigidity than putting a 5/8" shank into the hole & just pinching it with setscrews.

[JIMinPHX]

You might even just make up something like I pictured above & then mount a short boring bar in the end of it. This holder above would give you much better rigidity than the offset extension that you have in your picture.

[PatMarlin]

Well thanks for the input Jim.

Normally, I have the patience for this kind of stuff and I'm eager to deal with. It's just this one has been an ordeal starting a shop and machining from scratch with no hands on instruction, and having orders waiting and needing to get on with it already. I would be caught up last week if it wasn't for this last little PIA detail !...:mrgreen:

I have another tool from ISCAR (almost identical to the one in the pic) that I just bought called a "Duo Grip" that parts and turns that the ISCAR tech says will do the job plus it has a stronger locking seat that is better for turning. The one I have there now will part and turn as well, but it has a 4dgr lead angle with a sharp point and leaves an lousy finish turning because mainly the bit seat is not strong enough for the side pressures.

The new duo grip has a radius on the point so it should work BUT bits cost over $20 each. I'm trying to avoid going to that tool and use the tri-insert tool instead as I use that tool in most of my setups. Bits are $11 for three edges and I could get a quantity discount later on as well.

So hopefully, I can get this bar to work and send back the new ISCAR, but if all else fails- I'll use it and get to work.

[JIMinPHX]

A quicker & easier way to make a tool would be to braze a carbide chip onto the end of a steel shank. You can buy genuine braze-on chips for a few bucks or you can just use any old chip you have laying around. the genuine braze-on chips seem to hole up better in the long run.

You can also buy brazing rod in sheet form that you just cut to the size of the chip, place under it, add a little flux, & heat the whole mess with an acetylene torch to bond it together. This doesn't give you the quick change capability of a replaceable insert, but it gives you a workable tool with a lot less time & effort invested. I've made trepanning tools that way & cut through hundreds of inches of material before the tool needed to be sharpened.

[PatMarlin]

Yah, ya vee could do thot.

I'm still trying to picture the 4 jaw chuck offset in my mind and it just don't compute. Probably will when I get out there and start on it.

How do you insure your offset turning center is going to be dead on and over to the side of the bar so your insert stays flat?

[garandsrus]

Pat,

Check out this link... http://www.steves-workshop.co.uk/tips/lathetech/eccentrics/eccentricindex.htm

John

[KCSO]

First of all this is not a knock at Pat and so far he has gotten good advise. It is amazing to me that questions like these come up and usually from CNC folks when offset turning is like lesson #3 in South Bend's, HOW TO RUN A LATHE. Geeze if you had seen some of the jury rigging we did to get thinks built in the old lathes with a palmgren miling attachment ! As to the recess for the carbide insert in the lod days we would rough it out with a mill and finish it with a die sinking chisel. When I started making things on the lathe and milling head the first thinng I had to do was make my own tools, v blocks, jacks, wrenches, ect. In addition I had to learn to file parts to fit before i was allowed to touch a machine. Once again this isn't a knock on anyone just an observation.

My brother in Law can program a machine to cut out a hundred therbligs an hour, but if he can't program it he can't make one. I started in a blacksmish shop with hot iron and a file and I can't believe what we made with almost nothing.

[PatMarlin]

Thanks John- it makes sense now.

The offset adjustment jaw needs to be (Parallel if that's the correct term) with the tip point on my tool insert.

Eccentrics are very cool. It will come in handy.

[PatMarlin]

The good thing KCSO is I did start learning on a manual lathe, and will be doing this eccentric on my old Logan as well. Unfortunately, I have had no access to formal training.

The CNC is just for my die parts and that's it. I love working on the manual machines.

[PatMarlin]

For my needs CNC is just a means to crank out repetitive parts in a fast pace. It's like having a guy standing there working with you doing one thing and doing a great job at it.

I do all of my design work, and repairs etc on my manual machines, and strive to learn more and get better using them.

I also grind all of my own tooling on the manual machines. I have gone to inserts for the CNC for fast tool changes with no setup time. But I have to admit I'm cheap and still sharpen the bits when I can... :mrgreen:

[JIMinPHX]

If you decide to look into brazing together a tool of your own, you can find the carbide blanks on page 624 of this catalog - http://www1.mscdirect.com/CGI/NNPDFF?PMPAGE=624&PMCTLG=00

[Red River Rick]

There are "ADJUSTABLE" Boring Bars on the market. Valenite used to offer them when they were still in business, there are others.

Here's one manufacturer you may want to check out: http://www.criterionmachineworks.com/

RRR

[SPRINGFIELDM141972]

I don't want to over simplify the discussion here, but why not just heat and bend the rod to the degree off set you need. Yes, I know it will change the angle of engagement of the tool to the bore, but if it is chattering now a long angle engagement maybe what it will want to stop chattering. I'm not a carbide guy, but with HSS it sometimes helps to change the engagement angle.

Regards,
Everett

[xr650]

Pat,
Looks like you have a handle on your project.
Heres a pic if it helps.
http://www.fototime.com/7F7F2B53E3636BF/standard.jpg

Sometimes one chuck isn't enough.
http://www.fototime.com/523479BDE1DAADE/standard.jpg

It usually works out in the end.
http://www.fototime.com/A8EEF47F1CD4432/standard.jpg

There is an internal tapered thread in each end and a thru bore. :D

Sometimes your machine isn't big enough and you just have to forget about chuck jaws.
http://www.fototime.com/815DBA665500E36/standard.jpg

http://www.fototime.com/73301500188B82A/standard.jpg

[xr650]

I'm not a carbide guy, but with HSS it sometimes helps to change the engagement angle.


Yup, works with carbide too.

[JIMinPHX]

Valenite used to offer them when they were still in business,

Valenite went under?!?!?!?!

How did I miss that? Those guys made some good stuff.

[KCSO]

My FORMAL training was sweeping the shop and gettng to make things when the shop was closed. I'd make it and the smith would look at it tell me all that was wrong and have me make another one. When i could finally do something right i was allowed to make parts for other people.

I have a bunch of jigs for makinng parts on the faceplate. That last setup is how I did my Tru line Jr to standard thread.

Pat I still sharpen bits as i use a number of special shapes for gun work, crowning and such.

[PatMarlin]

You guys blow me away with that stuff... xr650- holy cow!

That is the finest type of education KSCO. For learning a trade, it don't get better than that.

That's how I learned and became a musician, and an audio record engineer- being able to start by sweeping the floor so to speak around people who were the real experts.

The good thing is I only need to able to do a good job on my products here. Lordy- at 50 trying to be a contract machnist would be to much. I got to give my brain a rest already. I wana go fishing ...:mrgreen:

[PatMarlin]

Well my bar didn't arrive yet. I made a practice piece and found .040 offset on the indicator is about the magic number I needed.

I cut a flat with my mill to make sure I could turn it correctly, then scribed the center line for a guide. Thanks for the help on this one fellas. I think it's going to work.

The old Logan 11x24 comes in pretty handy, and still does a quick decent job.


http://www.patmarlins.com/1eccentric.jpg


http://www.patmarlins.com/2eccentric.jpg


http://www.patmarlins.com/3eccentric.jpg


http://www.patmarlins.com/4eccentric.jpg


...


..

[xr650]

Looks good.
Piece of soup isnt it?

[frankenfab]

It is the old school Machinists that know alot of the good tricks. Obviously there is a good representation here of that group here. I learn from them every chance I get.

There's more than one way to skin a cat, but I would prefer the least amount of scratching and clawing on the way!:mrgreen:

[PatMarlin]

Got the bar today, and may turn it down tomorrow.

I'd like to thank my Cousin "Buckshot" here at CB. He was right there at the start helping me with a multitude of questions regarding tooling and machines, and general all around help to get me going... :mrgreen:

[machinisttx]

It is the old school Machinists that know alot of the good tricks. Obviously there is a good representation here of that group here. I learn from them every chance I get.

There's more than one way to skin a cat, but I would prefer the least amount of scratching and clawing on the way!:mrgreen:

When I was starting out, I had the opportunity and good fortune to learn a few things from those old fellows. 30+ years in the trade, doing things on manual equipment that some folks have a hard time figuring out on CNC, is a pretty good indication someone knows what they're doing. Most of those guys will share what they know if you're willing(and show some interest) to listen.

[scrapcan]

XR650,

I have to ask what that part was for? That is nice work. I am glad you guys are out there as it gives me a better feeling about some in our country being able to make things should be require it.

[PatMarlin]

I got the new bar offset turned and will give it a shot tomorrow. I hope it works.

[PatMarlin]

Update-

The 3/4" bar works excellent! Problem solved for $30...! and not to mention inexpensive bits. I sent the expensive ISCAR tool and bits back. $175 back in the account!

Thanks for the help everyone.

[xr650]

Pat,
Glad everything worked out for you.

Jeremy,
Our customer's customer had a well with parted casing. They could not get past the break so they thought it had shifted. They wanted a tool to enter the offset.
Our customer has a downhole indexer to line up this tool.
Our customer told me what they wanted. I designed it and helped with the setups. Didn't get to make any chips on this one though. The guy that I had build it thought I was nuts when I told him what we were going to make.
Our customer nor I thought this would work and as far as I know it didn’t. We got paid so all is good. It was a great teaching project.