Need Advice Turning Acralloy HT SRD

Nogoingback

Nogoingback

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So, I needed a piece of 2" OD round bar to make a short spacer the other day. Since I had none in the spares box, I asked my son who works part time at a
machine shop, if he could find something in the scrap bin and band saw a short length for me. (His boss is fine with this.) He brought it home, but had no
idea what the material was. Last night I began by facing off and immediately ran into problems with chatter, and rough surface finish. My best result was
with a HSS bit in a Diamond Toolholder, very little DOC, positive feed rate at a low spindle RPM, and lots of oil. He looked into what this stuff is, and it's Acralloy
HT SRD. Specs look like this:



acralloy.jpg

Acralloy® HT SRD G & P
HOT ROLLED & COLD FINISHED
PACIFIC ACRALLOY® has satisfied the high strength precision shafting requirements of the Pacific Northwest for decades. Acralloy® is drawn or turned then heat treated by quenching and tempering for high strength. It is then specially straightened, stress relieved, and ground and polished to 16 maximum rms. Acralloy® has good toughness as well as high strength and is the choice for many heavy duty shafting applications. It can be welded if properly preheated. Acralloy® can also be surface hardened by induction heat treating and by nitriding.

CHEMICAL COMPOSITION
Heat Analysis - ranges and limits %

C
.38/.45
Mn
.75/1.00
P
.035 max
S
.040 max
Cr
.80/1.10
Mo
.15/.25

TYPICAL PROPERTIES
Approximate - not for specification

Tensile (psi)
120,000
Yield (psi)
100,000
Elongation
20%
Hardness
255 HB
Machinability
55%


I've drilled it and need to bore the ID to 1.5", so before I begin I thought I'd ask for advice. My setup is a 1/2" carbide boring bar with triangular inserts. I have
both HSS and carbide inserts for this bar. Gibs all tightened up, compound replaced with a post, so as rigid a setup as I can make it. Depth will only be about
5/16" . Should I use carbide inserts and try running it fast, or HSS and run slower?, and what speeds should I aim for? The lathe is a 10" Logan.
I also need to part it off in the end. Any advice?

DSCF7359.jpg

Next time I'll probably just buy some 12L14! :)
 
For HSS, and RPM of about 300 will do. I prefer carbide myself. With carbide, as you bore the hole and it increases in diameter, you need to decrease RPM. Your approximate ranges will be about 550 to 900 RPM. You could split the difference and try 700 RPM as a starting point. Feed rate should be about 0.004" IPR.


I would recommend not parting that with your current chuck setup. Flip the jaws. The current setup is an open invitation to pushing the part out of the jaws. Might be a lot less hassle to cut it in the bandsaw.

Ray
 
Thanks Ray, I'll give that a try. I'll flip the jaws after I bore it and see how parting goes.
 
Part came out fine in the end. Bored it most of the way with carbide and switched to HSS for the finish pass. Surface finish was
better with HSS. Flipped the jaws around per Ray's suggestion and parted it off with a HSS tool, and then faced the part to square
it up. (Got some flex in my blade, so the face wasn't square.) . Parting was done dead slow in back gear with lots of oil and had
no problems. Learned a few things with this stuff, and hopefully my kid learned to check the material for me before he brings more
home.
 
Nogoingback said:
Part came out fine in the end. Bored it most of the way with carbide and switched to HSS for the finish pass. Surface finish was
better with HSS. Flipped the jaws around per Ray's suggestion and parted it off with a HSS tool, and then faced the part to square
it up. (Got some flex in my blade, so the face wasn't square.) . Parting was done dead slow in back gear with lots of oil and had
no problems. Learned a few things with this stuff, and hopefully my kid learned to check the material for me before he brings more
home.
Click to expand...

Do you happen to recall what feeds/speeds you used?

Ray
 
Can't give you exact numbers, but I used your suggested speeds as a starting point and then used the VFD keep the SFM fairly constant
as the ID changed. I fed by hand, so no clue. I found that the stuff was pretty sensitive to feed rate, so I just did what worked best. On
my lathe I had to keep the DOC very small to avoid chatter, so I made a lot of passes. When I parted off, I ran at 30 rpm, which is as slow
as my lathe goes at 60 hz. In the end the light finishing passes gave me
a reasonable surface finish, but while roughing out it was pretty nasty: kind of like what you can get with something like 1018. Kind of grabby
stuff. I think what this stuff needs is a machine that's really rigid.
 
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