Hello all and thanks in advance. I am pretty new to crank grinding I was recently trained by the last operator at a shop I work part time at. the last operator showed me proper radius on the grinding wheel and pretty much said to sweep to each side. I asked about the step radius on some cranks and really didn't get much respose. I have noticed occasionally after I grinding I have a nice bearing surface with a nice radius but then aslight step up and an OD corner. I try to bring the wheel out sweep in to the fillet and touch down to round the edge but I can't find any info on perfecting this part or what the radius is on allot of cranks. Thanks for any help. The last guy has been successful grinding for 12 years without problems but I'm a perfectionist and want it to be right
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Crank grinding newbe
- Thread starter Turbojim
- Start date
- Replies 26
- Views 6,597
crossthread
Titanium
- Joined
- Aug 5, 2004
- Location
- Richmond,VA,USA
I have no experience with grinding cranks (watched it done a few times is all) but generally when I am grinding, turning etc to a shoulder I want a slight radius to prevent a stress crack.
Matt@RFR
Titanium
- Joined
- May 26, 2004
- Location
- Paradise, Ca
None, or very few of us here are automotive machinists. You would be better served to ask your question at www.http://speedtalk.com/forum Be prepared for some debate amongst the members as to proper crank pin design.
Also, why the hell is your employer not setting standards for this? Do you not have a print to guide you? Who is your employer so I never buy a crank from them???
Also, why the hell is your employer not setting standards for this? Do you not have a print to guide you? Who is your employer so I never buy a crank from them???
Dan from Oakland
Titanium
- Joined
- Sep 15, 2005
- Location
- Oakland, CA
Your radius from the journal to the shoulder should be a smooth transition with no step. Leaving a step in the fillet creates a huge stress riser that will cause the crank to break. This is true in main and rod journals. You should have a radius dressing attachment for the machine there somewhere. Use it! Get a set of radius gages and check the crank before you grind it. The radius attachment has a feature to set the radius with a micrometer. Many a crankshaft has been ruined by a grinder that destroyed the fillets.Lots of shops don't like to maintain the original radius because 1) it takes time to dress the radius into the wheel and 2) wheels get used up faster depending on what radius is required. I always have a radius discussion with my crank grinder as a reminder that I want the radius maintained and I'll pay extra to make that happen.
Hope this helps. Dan
Hope this helps. Dan
JHOLLAND1
Titanium
- Joined
- Oct 8, 2005
- Location
- western washington state
a few thoughts on od crank grinding--also limited experience
most first regrind cranks are nitride or induction hardened--
try to reference trade literature to understand which process was used and
nominal rockwell hardness and--importantly--depth of process hardening on journal--this will have impact on metal removal if you penetrate hardened layer
spun bearing journals always loose hardness--outer layer of smear metal bonding is often present--grind wheel must be redressed more often
and a more porous open grain wheel used to debride
radius wheel dressing using single point ground diamond is likely preferable to form tool dressing
crush roll radius profiling is great option
use magnification to inspect diamond dresser and wheel radius
most first regrind cranks are nitride or induction hardened--
try to reference trade literature to understand which process was used and
nominal rockwell hardness and--importantly--depth of process hardening on journal--this will have impact on metal removal if you penetrate hardened layer
spun bearing journals always loose hardness--outer layer of smear metal bonding is often present--grind wheel must be redressed more often
and a more porous open grain wheel used to debride
radius wheel dressing using single point ground diamond is likely preferable to form tool dressing
crush roll radius profiling is great option
use magnification to inspect diamond dresser and wheel radius
CarbideBob
Diamond
- Joined
- Jan 14, 2007
- Location
- Flushing/Flint, Michigan
What type of cranks here? Certainly not high production automotive.
People I work with make millions of crankshafts and I do the pre-grind rough and semi tooling. I've never see one nitrated or induction hardened.
You do see this in specially work or smaller things like bikes and racers.
The world of 500,000 mile standard duty shafts is different that the go fast 100-200 hour stuff.
The print corner rad varies and some are undercut but the u-cut is usually on rods and not mains.
Best to measure the incoming part, no matter how bad it is damaged you can see what the original intent was.
Any slight step or ramp to the rad can be a problem, you need to know the chamfer on the bearing, plus or minus off the thrust guy, and not violate it this clear.
You want to be in free space. Once you are into this free space little matters.
Bob
JHOLLAND1
Titanium
- Joined
- Oct 8, 2005
- Location
- western washington state
my crank experience is 99% off road diesel--I had full Berco crank grind setup--sold to Chile--- now use cincinnati od
perkins, deutz, nissan, gm, etc
literature usually references hardening
perkins, deutz, nissan, gm, etc
literature usually references hardening
JS
Stainless
- Joined
- May 5, 2005
- Location
- Republic of Arizonia
It's been 18 years since I messed with automotive machining.
If it's not a smooth transition, it's wrong.
If it's not a smooth transition, it's wrong.
EmGo
Diamond
- Joined
- Apr 14, 2018
Bristol six cylinders were nitrided. Just sayin'
If it's nitrided tho, you're going through the case. Nitride is only a thou or two deep. Don't think it matters on car tho, unless it's a Model T it's got oil.
slowmotion
Cast Iron
- Joined
- Mar 31, 2013
- Location
- Danville Virginia
Are you dressing the radius with a hand held dressing stone or does the machine have a dedicated radius dresser? Not all machines, especially, pre 1980, had no dresser. Make and model of your machine would be helpful. I've ground cranks for 35 years and only recently gave it up. I have 8 wheels and hubs for all the different widths and radii you run into and that still isn't enough. Sweeping the journal to eliminate a step is an art, if you have that down then you are ahead of the game already.
slowmotion
Cast Iron
- Joined
- Mar 31, 2013
- Location
- Danville Virginia
Bristol six cylinders were nitrided. Just sayin'
If it's nitrided tho, you're going through the case. Nitride is only a thou or two deep. Don't think it matters on car tho, unless it's a Model T it's got oil.
BTW, I've ground many Bristol cranks (and it's BMW cousin the 327,328) and it was had to find one that wasn't cracked.
As I stated I'm at a learning stage and still grinding on practice cranks. And as you stated your not an automotive machinist in most cases you don't have prints or even proper radius specs. Duplicating what was there is a standard as far as I know . Our cranks are still being done by an outside source that is why I'm asking questions
Thanks Dan yes I have a radius dresser on the machine and also many radi gauges. I have been duplicating what is there but even then I'm not happy with some .
Grinder is an older storm 15a and yes there is a radius dresser . I am just not content with some of the fillet radius I have came across. I some cases from bearing surface out let's say there's a 2.4887 journal with an.075 radius then a step up to 2.987 similar to a thrust and probably .050 over to the fillet. The OD corner from thrust to fillet is not radiused it's almost square. I have been practicing running the wheel to the fillet itself and touching down on the thrust just enough to round that egde but that is an uneducated guess and I need to know the proper way. If there's a book or display I'm missing please let me know..thanks again
slowmotion
Cast Iron
- Joined
- Mar 31, 2013
- Location
- Danville Virginia
I think I understand what you are referring to. It sounds like you're talking about the area between the cheek (the 2.987 diameter you refer to) and where the crank is simply rough cast or forged. The machined cheek is always narrower than the width of the rod throw. No need to do anything way out there. The most important part of a radius is where it meets the crank journal, less so at the top of the radius where it blends into the cheek. Some grinders hit the radius on the way out, I've always done it on the way in. Most machines have a graduated table feed wheel (not sure on the 15) so it will reference exactly where the radius is. So on the final sweep, I can just barely touch the radius and pull out. If you plunge too heavily into the radius while the wheel is still on the journal on a final sweep, wheel chatter will transfer to the journal, leaving railroad tracks. If I've already blended the radii before finishing the journal, that never happens. How much do you leave for a final sweep?
Unfortunately the storm 15a does not have a graduated table feed makes it a little trickier but transfer your question normally about 2 to 3 thousands.
slowmotion
Cast Iron
- Joined
- Mar 31, 2013
- Location
- Danville Virginia
"Unfortunately the storm 15a does not have a graduated table feed makes it a little trickier but transfer your question normally about 2 to 3 thousands."
2-3 thou? 2-3 tenths is all I leave, did you mean tenths?
2-3 thou? 2-3 tenths is all I leave, did you mean tenths?
edwin dirnbeck
Hot Rolled
- Joined
- Oct 24, 2013
- Location
- st,louis mo
Also, why the hell is your employer not setting standards for this? Do you not have a print to guide you? Who is your employer so I never buy a crank from them???[/QUOTE]
I agree with you. However,the automotive machining world is entirely different. I have never seen a blueprint in an automotive shop.About 15 years ago ,I rebuilt my 350 chev corvette. The hot easy set up was a mild rebore and a stroke increased crankshaft,to increase size to 383 cu in. The crank must have been ruff ground and set in the sun for about a year. It was then finished ground and looked beautiful.On close inspection ,all the oil holes had hard baked on grinding swarf in them.It took me many hours of drilling and wire brushing with gun bore brushes to get it perfectly clean.I should have returned the crank. I bought it from a shop that had a good reputation.The next time I was there ,I complained. The owner just shrugged,like this is no big deal.I shudder to think,what would have happened if one little clump of grinding swarf would have been left in place Edwin Dirnbeck
I agree with you. However,the automotive machining world is entirely different. I have never seen a blueprint in an automotive shop.About 15 years ago ,I rebuilt my 350 chev corvette. The hot easy set up was a mild rebore and a stroke increased crankshaft,to increase size to 383 cu in. The crank must have been ruff ground and set in the sun for about a year. It was then finished ground and looked beautiful.On close inspection ,all the oil holes had hard baked on grinding swarf in them.It took me many hours of drilling and wire brushing with gun bore brushes to get it perfectly clean.I should have returned the crank. I bought it from a shop that had a good reputation.The next time I was there ,I complained. The owner just shrugged,like this is no big deal.I shudder to think,what would have happened if one little clump of grinding swarf would have been left in place Edwin Dirnbeck
Matt@RFR
Titanium
- Joined
- May 26, 2004
- Location
- Paradise, Ca
I get that, but buy a $2,000 crank for a race engine and you'll see a whole other world. That's why I asked who his employer is, so I never buy anything from them.
PackardV8
Hot Rolled
- Joined
- Jun 4, 2006
- Location
- Spokane, WA
I'm surprised a crank grinder operator with that much curiosity and a desire to do as perfect a product as possible is still employed. Usually, he'd be way too slow and be moved to another operation or put out on the street. Close enough is all most stock rebuild customers will pay for.
For example, in theory, the classic Chevy 350" mentioned above is a 90-degree-V8 crankshaft with four crankpins of equal stroke length and 90-degrees apart. In practice, if they finish grind with stroke within .003"-.004", close enough.
As far as getting the index right on, fuggediboudit! To index would take ten times as long and three out of four pre-2000 OEM cranks would go junk; wouldn't clean up at .030".
The newer generation of GM LS V8 cranks finished by CNC machinery is much closer on index than the old SBCs done on post-WWII machines.
Just a bit of trivia, but when Chevrolet got the V8 production line up and running in 1955, they added up the costs and each complete engine cost $59.
That the engine came to dominate racing was a surprise to Chevrolet Engineering. Their prime directive was to use as little cast iron as possible, as few moving parts as possible. The short, lightweight valve gear and head porting was a cost-saving measure. The original engine didn't use a big bolt to hold on the crank damper; a part which turned out to be needed.
jack vines
For example, in theory, the classic Chevy 350" mentioned above is a 90-degree-V8 crankshaft with four crankpins of equal stroke length and 90-degrees apart. In practice, if they finish grind with stroke within .003"-.004", close enough.
As far as getting the index right on, fuggediboudit! To index would take ten times as long and three out of four pre-2000 OEM cranks would go junk; wouldn't clean up at .030".
The newer generation of GM LS V8 cranks finished by CNC machinery is much closer on index than the old SBCs done on post-WWII machines.
Just a bit of trivia, but when Chevrolet got the V8 production line up and running in 1955, they added up the costs and each complete engine cost $59.
That the engine came to dominate racing was a surprise to Chevrolet Engineering. Their prime directive was to use as little cast iron as possible, as few moving parts as possible. The short, lightweight valve gear and head porting was a cost-saving measure. The original engine didn't use a big bolt to hold on the crank damper; a part which turned out to be needed.
jack vines
