ID grinding 360 brass?

Terry Keeley · Jan 10, 2022

Did a search but nothing came up.

S/C (green) wheels obviously but what grit?

They're about 1" ID sleeves that will be hard chromed and ground, finish isn't critical obviously but can't be too rough, I only have a couple thou to remove.

What about coolant? Type? Any other tips?

michiganbuck · Jan 10, 2022

I have Od and surfaced ground brass and found it to be a bugger with any wheel.
I would find a local grind shop to make your needed size and ream.

Or single point bore them with a very sharp tool bit. HSS would be better than carbide
About zero to 2* back rake, side 5 to 8, front 8 to 10 with a radial grind to miss the bushing Id.

QT: [I only have a couple thou to remove.]
Abrasive paper/cloth works better than grinding wheels.
Honing works better than grinding.

slippery coolants like oil or soapy water for grinding IMHO.

But are you grinding hard chrome?

Screwmachine · Jan 10, 2022

I think it would be pretty easy to hit dimension and a killer finish with almost anything besides grinding, is there a reason you want to grind the brass?

FredC · Jan 10, 2022

Screwmachine said:
I think it would be pretty easy to hit dimension and a killer finish with almost anything besides grinding, is there a reason you want to grind the brass?

Yeah, what SM said. Any cutting oil you use needs to be nonstaining. I have seen some real problems with plating when cutting oils with sulfur or other reactive additives were used on copper alloys. I have some brass parts that I lap with adjustable diamond laps and honing works well on the same parts. these maybe longer running production items than your need.

Terry Keeley · Jan 10, 2022

michiganbuck said:
I have Od and surfaced ground brass and found it to be a bugger with any wheel.
I would find a local grind shop to make your needed size and ream.

Or single point bore them with a very sharp tool bit. HSS would be better than carbide
About zero to 2* back rake, side 5 to 8, front 8 to 10 with a radial grind to miss the bushing Id.

QT: [I only have a couple thou to remove.]
Abrasive paper/cloth works better than grinding wheels.
Honing works better than grinding.

slippery coolants like oil or soapy water for grinding IMHO.

But are you grinding hard chrome?

Yes, will be finish grinding the chrome afterwards.

Screwmachine said:
I think it would be pretty easy to hit dimension and a killer finish with almost anything besides grinding, is there a reason you want to grind the brass?

Ya, thought about boring them but it's a very shallow tapered bore (0.001"/inch) and figure since I'll have to set up my grinder to do the chrome I'd like to test on the brass (have several junk pieces for setup), plus I figured I'd get a better surface finish. This will be done with a reciprocating grinder, I only need to do a few.

FredC said:
Yeah, what SM said. Any cutting oil you use needs to be nonstaining. I have seen some real problems with plating when cutting oils with sulfur or other reactive additives were used on copper alloys. I have some brass parts that I lap with adjustable diamond laps and honing works well on the same parts. these maybe longer running production items than your need.

Thanks, hadn't thought of that.

Screwmachine · Jan 10, 2022

Get the junk pieces chromed too and do your dialing in on those!

machinistrrt · Jan 17, 2022

I have jig ground aluminum but not brass. I imagine brass would be similar.
On aluminum, the best approach I found was to bore close, only leave a couple thousandths in the bore. Set up on the grinder, use a narrow contact patch, and wax the hell out of the wheel. feed a few tenths at a time, till you get the hang of it dress frequently.

Terry Keeley · Jan 22, 2022

machinistrrt said:
I have jig ground aluminum but not brass. I imagine brass would be similar.
On aluminum, the best approach I found was to bore close, only leave a couple thousandths in the bore. Set up on the grinder, use a narrow contact patch, and wax the hell out of the wheel. feed a few tenths at a time, till you get the hang of it dress frequently.

Thanks, never heard of using wax.

Are these what you mean?

Boelube Bl70200-13 Solids Lubricant - 1.6 Oz Push Tube | Aircraft Spruce Canada

G440 - KOOL GRIND SHARPENING LUBRICANT | Granberg International

FORMAX,FORMAX SAW BLADE WAX STICK,1-443-6056,KBC Tools & Machinery

Lubricating Stick Wax - 15 oz ID: LJ5515SK

Mcgyver · Jan 23, 2022

Unless some customer drawing is forcing this, imo its making a bunch of extra work being super precise before you are hard chroming,i.e. worrying about such a fine taper. Just have the chrome put on thick enough and worry about all the precision after chroming. If you do need to worry about it before hand for some reason I can't think of, another vote for sharp zero rake hss.

btw, the chrome grinding really benefits from using a CBN wheel which have their own tricks around dressing. Maybe you're an old hand at it and know this, but its something I just went so thought I'd pass it along

Terry Keeley · Jan 23, 2022

Mcgyver said:
Unless some customer drawing is forcing this, imo its making a bunch of extra work being super precise before you are hard chroming,i.e. worrying about such a fine taper. Just have the chrome put on thick enough and worry about all the precision after chroming. If you do need to worry about it before hand for some reason I can't think of, another vote for sharp zero rake hss.

btw, the chrome grinding really benefits from using a CBN wheel which have their own tricks around dressing. Maybe you're an old hand at it and know this, but its something I just went so thought I'd pass it along

Hobby alert, they're sleeves for my R/C boat engines.

I want to try a shallower taper and would end up grinding way more chrome than necessary if I don't open up the brass first.

I have a 170 grit CBN wheel but didn't use it last time I did these, just a 46 grit AO to rough and 90 for finishing.

I know about using a dressing stick to "clean" the CBN but is there a way to actually dress them true to the spindle? Would the CBN give a better finish on hard chrome than a 90 grit AO wheel? Any other tips?

Thanks.

Conrad Hoffman · Jan 23, 2022

Gotta ask, why do you need a taper? Seems to make an easy job much harder.

MCritchley · Jan 23, 2022

Conrad Hoffman said:
Gotta ask, why do you need a taper? Seems to make an easy job much harder.

That’s how model aircraft engines get their compression, tight at the TDC and loose at the bottom.

Terry, have you done any ID lapping? I would lap that sleeve before and after plating.

My guess is that is how most of the commercial manufactures do it. They would likely use a sunnen hone however. Your sleeve looks like it was touched on the face by a grinding wheel, perhaps the ID also. I bet the outfit that made that sleeve really understands the relationship between taper, size, and where TDC is. Most hobbyists just lap for a one off.

Terry Keeley · Jan 23, 2022

MCritchley said:
That’s how model aircraft engines get their compression, tight at the TDC and loose at the bottom.

Terry, have you done any ID lapping? I would lap that sleeve before and after plating.

My guess is that is how most of the commercial manufactures do it. They would likely use a sunnen hone however. Your sleeve looks like it was touched on the face by a grinding wheel, perhaps the ID also. I bet the outfit that made that sleeve really understands the relationship between taper, size, and where TDC is. Most hobbyists just lap for a one off.

I'm pretty sure they're done on some sort of ID grinder at the factory, guys have used a Sunnen hone but as I understand it they're really made to do straight bores and they somehow they grind and adjust the stones to get a reasonable taper.

I got an NSK reciprocating grinder and did a few of these years ago with some success, should be better now with my Super 11 lathe. A toolmaker buddy made a cast iron mount that allows it to be set on an angle for taper grinding and has a precision leadscrew so I can in feed to half a tenth or so (see post 5 above), lapping might work but would take forever.

And yes there's a very important relationship between taper and piston fit, also piston material (high silicone aluminum) and taper on the crown.

Mcgyver · Jan 23, 2022

this video is long but does explain CBN dressing fairly well, something I didn't know about but its got its own knack. May not be necessary if regular grinding wheels are working for you, but hard chrome is hard and I went CBN after not having the best time with a regular wheel. CBN wheels are expensive so you really want it mounted on a grinding hub....else you're eating up the wheel dressing it every time you used it. imo it has to be dressed, you can't just mound or you'll get the patchwork quilt grinding job.

Truing and dressing CBN wheel - YouTube

On the taper, if you're going through the plating into the brass when grinding the taper, couldn't you just do a thicker plate? smaller bore and add 5 thou to the plate thickness say. I assume you are sending it out and can specify the plate thickness?

Lapping tapers using a cylindrical lap at an angle could work - like the way watchmakers lathe bearings were done. Its just as complicated a set up as grinding, but you do get the best finish. I wouldn't think a tapered lap would work, you get no relative axial movement between lap and part so you can get rings etc

gappmast · Jan 23, 2022

FredC said:
Yeah, what SM said. Any cutting oil you use needs to be nonstaining. I have seen some real problems with plating when cutting oils with sulfur or other reactive additives were used on copper alloys. I have some brass parts that I lap with adjustable diamond laps and honing works well on the same parts. these maybe longer running production items than your need.

Sunnen has a honing oil, KG3X or MAN852, that have no sulfur or petroleum. They are basically vegetable oils. Taking a couple thou out of brass with a hone is fast.

Conrad Hoffman · Jan 23, 2022

Not a great thing for a Sunnen hone as they're really designed to eliminate taper, not cause it. I keep wondering if some sort of single blade reamer could be made to do it. An adjustable blade in a slot in a rod? Probably want to go out of round. Turning or grinding seems best. I like shear tools for OD work for a super finish, but I've never tried grinding one for ID work. A round carbide button on the end of a rod that's been ground at an angle might be interesting.

Terry Keeley · Jan 23, 2022

Mcgyver said:
this video is long but does explain CBN dressing fairly well, something I didn't know about but its got its own knack. May not be necessary if regular grinding wheels are working for you, but hard chrome is hard and I went CBN after not having the best time with a regular wheel. CBN wheels are expensive so you really want it mounted on a grinding hub....else you're eating up the wheel dressing it every time you used it. imo it has to be dressed, you can't just mound or you'll get the patchwork quilt grinding job.

Truing and dressing CBN wheel - YouTube

On the taper, if you're going through the plating into the brass when grinding the taper, couldn't you just do a thicker plate? smaller bore and add 5 thou to the plate thickness say. I assume you are sending it out and can specify the plate thickness?

Lapping tapers using a cylindrical lap at an angle could work - like the way watchmakers lathe bearings were done. Its just as complicated a set up as grinding, but you do get the best finish. I wouldn't think a tapered lap would work, you get no relative axial movement between lap and part so you can get rings etc

Very informative video, thanks! I'm going to true the 170 grit CBN wheel I got with the unit and give it a shot (it has it's own dedicated arbor). AO did work last time out but since the wheels are so small they tend to load up fast and need lots of dressing, maybe the CBN will be better.

Stock there's about 0.005" taper on the diameter from top to bottom, I want to reduce that to 0.002" but keep the finished I/D at the top the same so the heads fit tightly inside, therefore I'll end up taking out 1.5 thou per side at the top and will replace it with chrome.

LexD · Jan 24, 2022

Have you ground Hard Chrome before?

Terry Keeley · Jan 24, 2022

LexD said:
Have you ground Hard Chrome before?

I did some of these 25 years ago with the same grinder and a much smaller lathe.

Worked out well for the most part, I even chromed them myself.

Got any suggestions for a (relative) nooby?

swarfless · Jan 26, 2022

I thought when the ABC system was taken up about 50 years ago the brass cylinders were effectively 'finished' & simply 'flashed' with hard chrome .. one or two tenths. No post-chrome honing or lapping, the desired geometry set in the brass. Also believe it's the initial tenths are the hardest?

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