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How to (kinda) deep bore in AL

chasing_tenths

Hot Rolled
Joined
Jun 9, 2015
Part I'm trying to make: 1" OD 6061, sticking out about 4" from the collet. Drilled hole 12.0mm first. I have a 1/2 boring bar and I need to open it up to 18.0mm. Depth is almost 60mm. Boring bar is carbide and thru coolant using a CCMT-21.51 (Object moved). I previously tried this with a non-thru boring bar and I almost buried the thing. I have little experience on the lathe , so hoping someone will share some pointers.

My thoughts were 2 passes, one at 15mm and a second at 18mm. I figured the thru bit would get the chips out well... kinda. After a few parts run successfully, the thing got pretty jammed up deep on the first 15mm hole. I was able to scrape the crap off and change the insert. I was going full depth at the first diameter with 3 "pecks", then full depth at the second with 2 "pecks". Minimum hole diameter for the boring bar is 14.5mm, so really not much clearance at that first diameter.

After that, I thought to go more multiple depths (15, 30, 40, 50, 56) and do the larger diameter before going to the next depth on the smaller diameter. This seems to work better, but its still not inspiring confidence. I found a couple really long chips, so I'm thinking I should insert pauses to effectively peck. Previously, the "pecks" were a full retract out of the hole. My SFM is not very high (RPM 1500 or so), but I figured to do that because of the big stick out. I wonder I'm not approaching this right at all, but I don't know.

Should I be just going for one shot on the diameter (3mm radial chip) or should I be doing more lighter passes? The insert seems pretty tiny. Is pecking ok to do when boring or what's a better method to get the chips from getting too big?

Thanks
 

MaxPrairie

Hot Rolled
Joined
Jul 9, 2015
Drilling it out to 17mm will help alot and give the chips somewhere to go. You are basically plugging the hole with a 12mm and 1/2” bar.
 

mmurray70

Hot Rolled
Joined
Jan 11, 2003
You definitely need to drill way bigger. Personally id aim to drill it maybe 20-30 thou under and just take tiny skim. Less chips to deal with while boring the better.
 

kustomizer

Titanium
Joined
Aug 17, 2007
Location
North Fork Idaho
I had better results drilling as big a hole as mentioned above and boring from the back of the hole out to the face, if you need mort than one pass, stuff the drill back in to get the chips out then bore from the back out to the face again
 

chasing_tenths

Hot Rolled
Joined
Jun 9, 2015
I was going to specify in the first post, but deleted it. I didn't think EVERYONE would say drill it up ;) I cannot drill it up. I was doing that before, but swapped it out of the turret for the 1/2 boring bar which I need for other features, so I'm kinda stuck with the boring bar. Any suggestions considering no drill?

18.0 is rough, I finish it with a 3/8 boring bar that only does finish passes.

CCGT-21.51 seems the same as CCMT-21.51 except for tolerance class. How is that going to be any different?

Ok, I'm running it at 1000RPM and .006" chip which is under 200SFM.
 

doug925

Titanium
Joined
Nov 21, 2002
Location
Houston

chasing_tenths

Hot Rolled
Joined
Jun 9, 2015
Yes, 12.0 is needed for a deeper hole (8D drill). It also functions as the pilot for the bigger stuff.

I'm just trying to understand if I'm way off using the boring bar this way. I guess so?

I can swap it out for an 18mm drill, but then I have to do some other deep features with my finish 3/8 boring bar. I'll have to stick it out farther. My thought was have that one only do light finishing passes so the edge stays good for a lot of parts. The detail is a deep tapered feature about 15mm diameter. I'd only have to open it up from 12 with the 3/8 so maybe not too much extra work for it.

I'm not hearing any peeps about getting this done with the 1/2 bore, so maybe I'm on the wrong track trying to use it.
 

michiganbuck

Diamond
Joined
Jun 28, 2012
Location
Mt Clemens, Michigan 48035
knowing that likely you may have .0003 or better/more run out from ID to Od..if this OK.

Good to hand hold your bit/insert to a hole, perhaps washer to see that the bottom of the bit/insert will not rub at the bottom. To Fit/bore a 12mm rough bore you need to fit into the bore and have perhaps a radial relief with starting about 7* clearance and the heal not touching.

17mm (.669) drill rough bore will allow a stouter boring bar...for a finish of 18mm (.708).

Any reason you wish to not ream the bore?

Aluminum likes some positive rake at that side cutting edge...and some back rake would be good.


The part about 2 3/8" length/deep?

You can tool-bit scalp the start position of the drill

QT op [18.0 is rough, I finish it with a 3/8 boring bar that only does finish passes.]

Even more reason to ream it, or drill it...unless the price of the reamer is a problem.

A drill will cut about .0002 or so larger than the micrometer size. may cost 8 to 20 bucks.
 

CITIZEN F16

Titanium
Joined
May 2, 2021
I am confused, why not just replace the 12mm drill with a 17.5mm or so? How many parts are you making? The chances of
chip packing are high no matter how many passes you are making considering the hole size and boring bar size.
 

chasing_tenths

Hot Rolled
Joined
Jun 9, 2015
The part has a deep 12.0 hole. Less deep it's just over 18 with a weird tapered transition. I think I give up. I'm not seeing anyone say 1/2 bore is a good choice. I'm going to get a carbide tipped S&D 23/32 and ditch the 1/2 bore. Do the finish pass and deep detail with the 3/8 finisher. Possibly quite a few and I'm going to bar pull, so I want to be able to walk (not far) away and let it run.
 

chasing_tenths

Hot Rolled
Joined
Jun 9, 2015
I thought reamer on a lathe was a nogo? I'm not sure I want to see the quote for a custom long stepped carbide drill or reamer.
 

Nagol

Aluminum
Joined
May 21, 2020
Rather than an expensive reamer why not get a cheaper step drill with a 12mm point and 17.5 to rough out the bore. Then your boring bar of choice to finish the 18MM bore
 








 
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