# Boring Issues



## freeqgeek (Mar 29, 2018)

Evening Guys-

Making my first real attempt at boring something other than aluminum and am running into issues. Hoping someone here with a lot more knowledge than I can tell me where I am going wrong.

I am working with stainless round stock. Diameter of 1” and 6” in length that is running true in the 4-jaw with +/- .002 TIR. I have a 3/8” boring bar with carbide insert installed in the QCTP and hanging out just a hair over 3”, which when I rotate the stainless should allow me to bore the entire length. I drilled out the stock with a 1/2” drill bit and am now attempting to bore it the remainder with a plan of leaving a wall thickness of .01”.

So here is the problem… God awful chatter and a terrible finish. I have tried adjusting the speeds and feeds. Double checked that my tool is on center. Reduced the tool hangout down to 1”. Tried running dry as well as the other extreme end with way too much oil. Swapped the insert for a fresh one. No matter what I try I get a terrible squeal, chatter, and the finish is not even close to usable.

Would appreciate any advice you guys have to offer.

Thanks!


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## ttabbal (Mar 29, 2018)

What size QCTP? AXA?

What lathe? 

What depth of cut? Which type of stainless?


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## freeqgeek (Mar 29, 2018)

The lathe is a PM-1236 running with a BXA tool post, and I have tried everything from .0050" to .0100" depth of cut.


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## ttabbal (Mar 29, 2018)

You didn't say what stainless you have, and I'm a noob who has only worked one type, so you might try it, but hopefully someone more experienced offers advice. 

The stainless I have work hardens easily and you need to take deeper cuts to prevent it. It's counter-intuitive, but cutting about 0.020" worked best for me. And my lathe is lighter than yours, PM-1127. My steel is 304. 

If you have scraps available, you should be able to test outside a bore as well with the same boring bar. It might help you dial in the cut before working on your part. 

Some tips I was offered when I had some trouble with SS. https://www.hobby-machinist.com/threads/machining-304-stainless.67116/


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## T Bredehoft (Mar 29, 2018)

freeqgeek said:


> I have a 3/8” boring bar with carbide insert i



there's the source o f your chatter. Drill the hole out to .875 and bore the rest in four or five passes.


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## benmychree (Mar 29, 2018)

With a wall thickness of only .010 (finished) you are likely to have nothing but trouble; one thing that would help greatly is to switch to 303 stainless; if the part is hanging out of the chuck that far, use a steady rest, but bottom line, the wall thickness is going to defeat any sort of precision job being possible.


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## 100LL (Mar 29, 2018)

I don’t find this issue at all boring.  Quite the opposite


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## mmcmdl (Mar 29, 2018)

Think I would have gotten larger stock and drilled then reamed that ID to size . Then use plugs and turn the OD down concentric to the bore . JMI . 

AND , I just saw a .010 finished wall thickness ? Better fill that bore with something , lead shot , bbs etc , to help stabilize that wall cuz it will chatter !


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## westerner (Mar 29, 2018)

Indeed. Boring is NOT a boring subject to me. I have only a few boring jobs under my belt, and they were anything BUT!


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## freeqgeek (Mar 30, 2018)

ttabbal said:


> You didn't say what stainless you have, and I'm a noob who has only worked one type, so you might try it, but hopefully someone more experienced offers advice.
> 
> The stainless I have work hardens easily and you need to take deeper cuts to prevent it. It's counter-intuitive, but cutting about 0.020" worked best for me. And my lathe is lighter than yours, PM-1127. My steel is 304.
> 
> ...



Thanks for the link. That is really helpful. 

I don't honestly know what type of stainless it is. I managed to dumpster dive at a local shop and pay twenty-five cents a pound for anything I wanted. Found quite a bit of useful material, especially for someone just starting out. Gave me the opportunity to make mistakes without wasting expensive material...


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## freeqgeek (Mar 30, 2018)

T Bredehoft said:


> there's the source o f your chatter. Drill the hole out to .875 and bore the rest in four or five passes.



Unfortunately I don't have a drill that goes up to that size but plan on acquiring a couple larger bits tomorrow. So this is likely the route I am going to take.


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## freeqgeek (Mar 30, 2018)

mmcmdl said:


> Think I would have gotten larger stock and drilled then reamed that ID to size . Then use plugs and turn the OD down concentric to the bore . JMI .
> 
> AND , I just saw a .010 finished wall thickness ? Better fill that bore with something , lead shot , bbs etc , to help stabilize that wall cuz it will chatter !


I have been looking at reamers recently. They can get quite expensive... Do you have a preference for straight or spiral flutes and is there a benefit of one over the other?


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## rock_breaker (Mar 30, 2018)

It wasn't said but a larger boring bar may improve the rigidity. No experience with stainless so lots of luck.
Ray


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## Liljoebrshooter (Mar 30, 2018)

A larger bar would probably help a lot.
One way to get rid of the chatter is to move the bar into the bore and cut grooves by hand, feeding the cross slide out. Make a cut, move left a small amount,  make a cut, over and over again.  
Joe Hynes


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## Liljoebrshooter (Mar 30, 2018)

Oh and 304ss can be a real  bit#$ to get a good cut. But it can be done.


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## Liljoebrshooter (Mar 30, 2018)

You didn't say what style bar and insert you were using,  but I would guess a CCMT.   That is most likely the problem.  With the 304 you would be better off with a sharp edge cutter of some style.


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## freeqgeek (Mar 30, 2018)

Liljoebrshooter said:


> You didn't say what style bar and insert you were using,  but I would guess a CCMT.   That is most likely the problem.  With the 304 you would be better off with a sharp edge cutter of some style.


I have been wondering about this actually. I am a bit of a junkie and always wanting more tools... 

Dead on. I am currently using the CCMT style. But with so many other shapes I don't know where to begin. What insert style would you recommend for SS?


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## Liljoebrshooter (Mar 30, 2018)

I have the best results with a ccgt insert.  You have to figure out if the bar will accept them.  They have more angle to them and some of the pockets won't fit them right and when you tighten the screw down they break.  Ask me how I know that. 
I  also have the best results with a solid carbide bar,  the micro 100 ones.  They are expensive and very unforgivable.  If you crash them they just snap like a toothpick.  I got a few of them on the  bay for a few bucks each. 
Joe Hynes


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## Liljoebrshooter (Mar 30, 2018)

Here are some telescoping stands I have made.  Lots of boring on the bushings for these.


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## Liljoebrshooter (Mar 30, 2018)

This is what I'm making.


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## magicniner (Mar 30, 2018)

freeqgeek said:


> I drilled out the stock with a 1/2” drill bit and am now attempting to bore it the remainder with a plan of leaving a wall thickness of .01”



You may be better using Soft Jaws or a Collet Chuck to hold that, a 10 thou wall thickness is going to be all over the place if you hold it with a conventional chuck


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## TakeDeadAim (Mar 30, 2018)

If your wanting to end up with a .980" ID have you thought of starting with thin wall tubing?  Thats a lot of stock to remove even at .020" a pass if you can get that small dia. boring bar to tolerate it to a 3" depth.  .930" ID tube is available in 304 stainless for about $7 a foot and no I don't sell tubing.


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## Mitch Alsup (Mar 30, 2018)

freeqgeek said:


> I am working with stainless round stock. Diameter of 1” and 6” in length that is running true in the 4-jaw with +/- .002 TIR. I have a 3/8” boring bar with carbide insert installed in the QCTP and hanging out just a hair over 3”, which when I rotate the stainless should allow me to bore the entire length. I drilled out the stock with a 1/2” drill bit and am now attempting to bore it the remainder with a plan of leaving a wall thickness of .01”.
> 
> So here is the problem… God awful chatter and a terrible finish.





freeqgeek said:


> The lathe is a PM-1236 running with a BXA tool post, and I have tried everything from .0050" to .0100" depth of cut.



Drill to 0.500,
Bore to 0.650 with 3/8 (9.5mm) boring bar,
Switch to 16mm boring bar (largest that fits BXA) for the rest of the job.

3/8s is never going to be stiff enough with the nose length you need here.
You always want to use the largest boring bar that you can make fit the hole.


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## chips&more (Mar 30, 2018)

I understand your problem. And I have been doing that kind of operation successfully. The trick is to wrap the outside of the material with Duct-Seal (HVAC folks use it). It kills the harmonics. And it would also help to use a solid Carbide boring bar. I see no problem if done this way. The chatter will be gone…Dave.

You may need to wrap tape around the Duct-Seal if it starts to fly off.


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## mksj (Mar 30, 2018)

I think you will be hard pressed to bore metal to a wall thickness of 0.01" over 3", in particular with SS. Standard steel boring bars, you can bore to a depth of 3-4X the bar diameter so for 3/8" you are talking maybe 1.2". Carbide boring bar 6-8X the diameter, but they can snap very easily. If boring just under 1" ID to a depth of 3" you would need something like a 5/8" carbide boring bar. Still, I would expect the tube to collapse or snag on the boring bar with the wall thickness you are targeting. You might look at thin wall tubing like below with a 1" OD and a 0.035" wall thickness, it is 1/2 the price of solid stock. I do not know the uniformity you are looking for as to wall thickness tolerance and straightness.
http://www.speedymetals.com/pc-4492-8276-1-od-x-0035-wall-tube-304-stainless-steel-annealed.aspx

I am not a fan of using tape on any part to hold it in the lathe chuck or collet, if anything I have found that taped parts slip more readily and it makes a mess. I use brown paper bag strips or a wrap it around a part to prevent movement and minimize part damage. But in this case I would be more inclined to use something like an ER40 collet system that would hold around the part, but I still think the wall thickness is too thin and it would deform. CCGT insert in a 5/8" boring bar would most likely be a 32.51, you want a small tip as the larger tip will chatter. I do not do much with stainless, but I use these CCGT uncoated inserts in a wide range of metals with good results for light cuts. https://www.ebay.com/itm/10pcs-CCGT-32-51FN-25P-H210T-CERATIZIT-ccgt-09t304fn-25p-h210t/291946846515


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## magicniner (Mar 31, 2018)

Can all the guys who haven't mentioned it tell us how you're boring a _Six Inch Long Part,_ with a _10 Thou Wall_, it must be so easy for you that you've forgotten to mention it in your suggestions of how to tackle this job but I for one would love to add that knowledge to my workshop log.


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## Timboberonion (Mar 31, 2018)

So you want to end up with a 6 inch long, ~ 1" diameter tube with a .010" wall? I guess it can be done, but you would start with oversize stock, say 1.25". Bore it to .990, you need bigger than 3/8 to get to 3" without chatter. Fill the bore with low melt metal to stabilize(Wood's metal?). Then turn the outside to 1.00. Melt the filler out and hopefully it doesn't turn into a twizzler. 

Or just buy thin wall tube.


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## Capt45 (Apr 1, 2018)

Here's how Joe Pie does it:


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## bfd (Apr 2, 2018)

what I have found is that once the chatter is there its harder to get rid of. start off slow, use cutting oil, you can add a weight to the bar to cut down on vibration and wrap the o.d. of the part with rubber, old bike inner tubes secured with hose clamps will also dampen vibration. no radius on the tool bit. to rid yourself of the existing chatter go as slow as the lathe will allow, I have even turned the lathe by hand. hope this gives you some ideas bill


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## Billh50 (Apr 2, 2018)

I have turned and bored a few parts with thin walls in the past. I found the best way to stop chatter was to wrap the outside with a heavy elastic band for small stuff and a rubber bungee for the larger stuff. It keeps the harmonics down to a point that there is no noticeable chatter. I learned this trick when I was learning automotive machining. They always wrapped the brake drums with rubber straps when boring the ID.


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## freeqgeek (Apr 2, 2018)

chips&more said:


> I understand your problem. And I have been doing that kind of operation successfully. The trick is to wrap the outside of the material with Duct-Seal (HVAC folks use it). It kills the harmonics. And it would also help to use a solid Carbide boring bar. I see no problem if done this way. The chatter will be gone…Dave.
> 
> You may need to wrap tape around the Duct-Seal if it starts to fly off.


Leaning towards a collet chuck system, but this is interesting. If nothing else I might just have to try it. I would have never thought of duct-seal. MKSJ also suggest a brown paper bag. I really love the simple innovations that this group brings forward


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## freeqgeek (Apr 2, 2018)

Timboberonion said:


> So you want to end up with a 6 inch long, ~ 1" diameter tube with a .010" wall? I guess it can be done, but you would start with oversize stock, say 1.25". Bore it to .990, you need bigger than 3/8 to get to 3" without chatter. Fill the bore with low melt metal to stabilize(Wood's metal?). Then turn the outside to 1.00. Melt the filler out and hopefully it doesn't turn into a twizzler.
> 
> Or just buy thin wall tube.


You are the second person to suggest just buying tube, which I agree is totally logical. And if I were running a shop and had years of knowledge already, thats probably what I would do. If I needed something quickly for a customers order it wouldn't make a lot of sense doing what I am doing. Bottom line is that I have a LOT of learning to do and a ton of scrap metal laying around to experiment on. So taking a scrap piece of SS and boring it gives me the opportunity to gain experience, ask a lot of questions of this group, myself, and my equipment, and learn a lot. Not to mention that it is a challenge for me. I also love that it gives my brain something to noodle


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## freeqgeek (Apr 2, 2018)

Just a quick thanks to everyone. This board is freaking amazing. Appreciate all of you sharing your knowledge with those of us still trying to figure things out.


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