ID grinding 360 brass?

[Terry Keeley]

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?

Not sure about 50 years ago but the last 30 or so anyway it's been about 0.002" of finished hard chrome (1100 Hv) per side.

Lots of other two stroke stuff with rings have flash plated Nikasil cylinders.

 

[swarfless]

Hi Terry, the chap I knew that used to manufacture Taipan model engines here used to grind the bores on a semi-auto Weiler internal grinder, programmable (have never found any reference to those subsequently) to establish the desired taper, then manually hone (Delapena) to achieve a nice fine cross-hatch without removing enough metal to correct the taper. All the ABCs in those days were plain un-ringed pistons .. definitely late '60s early '70s. Relying on memory here.

 

[Terry Keeley]

Hi Terry, the chap I knew that used to manufacture Taipan model engines here used to grind the bores on a semi-auto Weiler internal grinder, programmable (have never found any reference to those subsequently) to establish the desired taper, then manually hone (Delapena) to achieve a nice fine cross-hatch without removing enough metal to correct the taper. All the ABCs in those days were plain un-ringed pistons .. definitely late '60s early '70s. Relying on memory here.

Funny how things change, now we're looking for a mirror finish and it's all about matching the taper on the piston crown to the taper in the liner, piston material and how hot the motor runs.

I remember those Tiapan motors back in the 70's, never saw one but heard they were quite good at the time.

 

[swarfless]

By 'fine' cross-hatch I mean more optical than actual grooving. Yeah I think it was the ABC Taipan that broke the business. Could be wrong, Gordon had retired & moved to Queensland, I had moved to another different one, so my recollections at that point are hearsay, the business was in new hands, I had been long out of the game at that stage. We were using tapered bores in our team racing Taipan diesels tho' in my day .. our rough & ready criterion was 'squeak tight' at top dead centre, using parallel cylindrical centreless ground Meehanite pistons. You're right, things have changed .. as they should.

 

[machinistrrt]

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

What I used was solid AccuLube, looks like a blue bar of soap. Nontoxic, and works.

 

[machinistrrt]

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

I never had access to CBN wheels for jig grinding. I didn't catch the chrome requirement; I'd revise my advise to just bore to a dimension that'll result in .002-.004 chrome at finish. alum oxide wheels will work ok, but require frequent dressing-for just a couple of parts, doesn't pay to get CBN.

 

[Terry Keeley]

What I used was solid AccuLube, looks like a blue bar of soap. Nontoxic, and works.

Thanks, got some of this on the way:

 

[Terry Keeley]

Just an update and huge thank you to machinstrrt for the Accu-Lube suggestion, I'm using a 46 grit SiC wheel with the wax plus coolant and it's not clogging up at all.

I only need to take out 0.002" per side to get them ready for chrome and might be able to do all nine of them with only a dressing or two.

Here's a quick video of my set up (caution - hobby alert!):