Boring Issues

[magicniner]

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

 

[TakeDeadAim]

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.

 

[Mitch Alsup]

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.

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.

 

[chips&more]

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.

 

[mksj]

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

 

[magicniner]

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.

 

[Timboberonion]

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.

 

[Capt45]

Here's how Joe Pie does it:

 

[bfd]

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

 

[Billh50]

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.