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Boring bar setup question
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Hi group!
I recently bought a 3/8 indexable boring bar that uses CCMT inserts. The bar has 5° negative built in. I'm using CCGT high polish 21.51 inserts and have a huge amount of chatter. I'm doing a 3/4 inch diameter hole just over 3" deep in 6161 aluminum. I've tried the bar above center and on center. Above seems to chatter a bit less but I still can't get a nice cut. Wrong insert, bad setup? Do I need a different bar? Just too deep of a hole and I'm going to have to live with it? Any tips, tricks, hints, etc will be greatly appreciated! Ryan |
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There's a great article on boring bar chatter:
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A lot of math tho... Long thin boring bars are prone to that. Some comments here: Do you have a larger diameter boring bar? That may help... Also - tunable boring bar article: Basically add some mass to change the resonant frequency ... Ryan_Hodges wrote: Hi group! |
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Thanks! I'll read the .pdf's when I get home.
One thing I see from the thread is I may have got the wrong inserts. I probably should have got 20.50's with the .008" nose instead of 20.51's with an .016" nose. WAM <ajawam2@...> wrote: ? There's a great article on boring bar chatter: |
开云体育Hi Ryan !
For good results, boring holes are typically limited to about 1.5-2x boring bar diameter. As such, a 3/8 boring bar is only good to about 1/2 inches. After this it will chatter with variable results. All lathe tools work well only upto about 1-3x their size. Ie a 1/2 inch tool will only work well to 1-1.5 inches deep. However.. Alu is easy. Your problem is rake. CCMT is 7 degrees positive and you need to maintain this, *especially* when doing deep bores. With a -5 degrees boring bar, you are losing the benefits of the insert, and greatly increasing the problems of the overly long, slim, thin bar. It *can* be done with a 3/8 in alu but not well, imo. You need to have at least 7 degrees rake, even? a bit more. If you can make (buy) another bar (any steel) of near .7 inches, and have the bit be at zero-1 degree rake, it will go vastly better. For alu, at .75 inches or about 18 mm, I would recommend about 1000 rpm, 0.1 - 0.06 mm cuts. ? -- -hanermo |
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John Lindo
Hello Ryan. You did not mention if this was a through hole that you have problems with. If it is a blind hole,a boring bar with a flood coolant hole may work,to wash out the chips. I agree with the comments about rake angles. IMO carbide for cutting?aluminium never seems to work well.the chips tend to stick to the tip even with WD 40 as a cutting lubricant. Try using a home made boring bar with a HSS tool bit.,and or a D bit drill made out of 3/4 " drill rod. Just for interest,how did you get the hole roughed out in the first place? If a through hole have you thought about boring from both ends,skimming the outside diameter and using a soft jaws in a 3 jaw chuck, or a 4 jaw chuck, using a Dial indicator to get the concentricity when boring from the other end. John L Spain.
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Thanks!
Do you think a "P" insert (11°) would help? It's only 6° but better than the 2 I have now. cnc sales <gcode.fi@...> wrote: ?
Hi Ryan !
For good results, boring holes are typically limited to about 1.5-2x boring bar diameter. As such, a 3/8 boring bar is only good to about 1/2 inches. After this it will chatter with variable results. All lathe tools work well only upto about 1-3x their size. Ie a 1/2 inch tool will only work well to 1-1.5 inches deep. However.. Alu is easy. Your problem is rake. CCMT is 7 degrees positive and you need to maintain this, *especially* when doing deep bores. With a -5 degrees boring bar, you are losing the benefits of the insert, and greatly increasing the problems of the overly long, slim, thin bar. It *can* be done with a 3/8 in alu but not well, imo. You need to have at least 7 degrees rake, even? a bit more. If you can make (buy) another bar (any steel) of near .7 inches, and have the bit be at zero-1 degree rake, it will go vastly better. For alu, at .75 inches or about 18 mm, I would recommend about 1000 rpm, 0.1 - 0.06 mm cuts. ? -- -hanermo |
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Hi John.
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Yes, its a through hole. A couple of them actually. One starts as solid bar, drilled to 1/2" then bored out to .625" or so to the proper depth to leave a .480" section with the 1/2" hole. This part goes over a stepped shaft. The other starts with a .750" hole (I buy the material that way) and is bored out a bit to thread 13/16 x 26. When it's all said and done the first part ends up turned and threaded for the second to screw over to become one piece. It's actually a handle upgrade. I'll have to search D drill. I don't know what that is. And I don't have any way to make a HSS bar. By the way, I've tried HSS inserts and have horrible chip welding. Do I just have crap steel inserts? Carbide has been so much better. Thanks, Ryan John Lindo <bechetboat@...> wrote: ? Hello Ryan. You did not mention if this was a through hole that you have problems with. If it is a blind hole,a boring bar with a flood coolant hole may work,to wash out the chips. I agree with the comments about rake angles. IMO carbide for cutting?aluminium never seems to work well.the chips tend to stick to the tip even with WD 40 as a cutting lubricant. Try using a home made boring bar with a HSS tool bit.,and or a D bit drill made out of 3/4 " drill rod. Just for interest,how did you get the hole roughed out in the first place? If a through hole have you thought about boring from both ends,skimming the outside diameter and using a soft jaws in a 3 jaw chuck, or a 4 jaw chuck, using a Dial indicator to get the concentricity when boring from the other end. John L Spain.
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开云体育I have never had problems boring or
cutting alu with any of 3 different insert types, from various
manufacturers in various sizes.
Alu is easy, ime. ? |
开云体育I think it would work fine.
It?s neither rocket science nor too hard, Just some positive rake and thats it. On 03/02/2013 19:59, Ryan Hodges wrote: |
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Thanks.
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I've actually had some good results flipping the bar over to the flat milled on the bottom and cutting on the back side of the work. I set the bar low (high on the cut) and it actually looks like a lathe cut it, not chipped out with dull deer antlers, hahaha! cnc sales <gcode.fi@...> wrote: ?
I think it would work fine.
It?s neither rocket science nor too hard, Just some positive rake and thats it. On 03/02/2013 19:59, Ryan Hodges wrote: ? |