HELP! Stroker crank

[srcarr52]

I have an old Milltronics 00 CNC knee mill that keeps rocking out some pretty decent parts. I did upgrade it to a newer version of their CENT 5 software which isn't as easy to use the MDI mode vs. the CENT 1 but has better conversational programing cycles.

 

[Rich Fife]

I have an old Milltronics 00 CNC knee mill that keeps rocking out some pretty decent parts. I did upgrade it to a newer version of their CENT 5 software which isn't as easy to use the MDI mode vs. the CENT 1 but has better conversational programing cycles.

I'm not familiar with it...

Our new Prototrak is pretty sweet... it's a DPM RX5... I dont know if I'd take it over a Haas, but, i also wouldn't turn it away.

 

[Al Smith]

I think the subject while being interesting is not one to be experimented with by a hobby machineist .You have to remember it's a pressed together rotating assembly with a one piece connecting rod .Not that it's impossible because Falicon does it all the time on snow mobiles and 140 CC Husky 3120 race engines . However that's what they do so they should be good at it .
For example way back when the air was clean and sex was dirty they made 80 strockers from standard Harley parts but they had use spacers under the cylinders to keep from driving the pistons through the cylinder heads .Which is another thing to think of .Nothing just as simple as moving the crank throw with the pin . 2 cents no more no less .

 

[Firewood Hoarder]

My manual mill is a King Rich with a 12x50 table. The guys who set up our new DPM RX7 a few years ago said I can retrofit the machine I already have, as the prototrak machines all use King Rich castings (look for the KR cast into them) .

Be cheaper and easier to just find a good used unit, though. I still need to get more power into my shop for my lathe, first. Don't have the amperage for a 7.5 hp motor and enough phase converter yet

 

[srcarr52]

I'm not familiar with it...

Our new Prototrak is pretty sweet... it's a DPM RX5... I dont know if I'd take it over a Haas, but, i also wouldn't turn it away.

It's a pretty nice machine for 1996, it's built on a large Tawain casting knee mill frame with a 5hp spindle motor. Milltronics patented putting a 6.5" vertical slide behind the mill head so you maintain the use of the manual quill. At that time they also had some pretty awesome conversational programming based on parameterized g code and it's a DOS based PC control with DC servo motors.

I wish I would have found one with the CAT 40 spindle instead of the R8 as I've had issues with tools getting loose or not enough rigidity to take really deep cuts. If I stick to lighter finish passes I can make very precise parts.

I also have a '98 Partner 1 which I need to get running. It is a full cabinet mill with a 10hp spindle and 12 position tool changer.

 

[Hulpio]

My manual mill is a King Rich with a 12x50 table. The guys who set up our new DPM RX7 a few years ago said I can retrofit the machine I already have, as the prototrak machines all use King Rich castings (look for the KR cast into them) .

Be cheaper and easier to just find a good used unit, though. I still need to get more power into my shop for my lathe, first. Don't have the amperage for a 7.5 hp motor and enough phase converter yet

So 3 x 25A 3phase 400VAC is not available? We have 230VAC between phase and neutral. Then 400VAC between phases. This is pretty much minimum std for any house.

 

[Firewood Hoarder]

So 3 x 25A 3phase 400VAC is not available? We have 230VAC between phase and neutral. Then 400VAC between phases. This is pretty much minimum std for any house.

The standard where I live is 240v, single phase into a home. No 3 phase power is available where I live, to a residence. This is common throughout the US.

So I will have to run a phase converter to create 3 phase power, to run my lathe appropriately.

 

[Ketchup]

I think the subject while being interesting is not one to be experimented with by a hobby machineist .You have to remember it's a pressed together rotating assembly with a one piece connecting rod .Not that it's impossible because Falicon does it all the time on snow mobiles and 140 CC Husky 3120 race engines . However that's what they do so they should be good at it .
For example way back when the air was clean and sex was dirty they made 80 strockers from standard Harley parts but they had use spacers under the cylinders to keep from driving the pistons through the cylinder heads .Which is another thing to think of .Nothing just as simple as moving the crank throw with the pin . 2 cents no more no less .

I don’t understand why it shouldn’t be attempted by a hobby machinist. Sounds like fun to me.

It also appears there are at least three career machinists in this thread. It’s a good one guys! Thanks for the info!

 

[srcarr52]

I don’t understand why it shouldn’t be attempted by a hobby machinist. Sounds like fun to me.

It also appears there are at least three career machinists in this thread. It’s a good one guys! Thanks for the info!

It just takes time to make everything. You have to make some plates/fixtures to press chainsaw cranks apart as they are too small to sit on normal press plates. You can get by pressing them back together without a fixture but using one gets you much better initial crank run out.

 

[Al Smith]

I wasn't saying it's impossible to do just beyond the capability of most people .For that matter I bored out the cylinder for a Mac 125 and made and installed a grade 50 cast iron sleeve .Using a Bridgeport model M milling machine ,circa 1940 with a boring tool made from a morter mixer paddle axle .That literally took weeks to complete . I'm self taught on machine tools and do okay for a novice but I've been at it since I was about 15 years old,over 60 years ago .---I'm an old fart .

 

[Rich Fife]

It just takes time to make everything. You have to make some plates/fixtures to press chainsaw cranks apart as they are too small to sit on normal press plates. You can get by pressing them back together without a fixture but using one gets you much better initial crank run out.

View attachment 409855 View attachment 409858

Nice work!!!

I was too impatient to build a fixture for the YZ450F crank... i went old school... machinist square and scribe marks... I had .010" of total run out... took me about 1-1/2 hrs to get it dialed. Needless to say, this guy will be machining a fixture for the YZ250F crank.

 

[srcarr52]

Nice work!!!

I was too impatient to build a fixture for the YZ450F crank... i went old school... machinist square and scribe marks... I had .010" of total run out... took me about 1-1/2 hrs to get it dialed. Needless to say, this guy will be machining a fixture for the YZ250F crank.

I just pressed one together with that crank press, it was spot on timing wise and I just had to spread the lobes a little to get rid of the 0.003" initial run out.

 

[Rich Fife]

I just pressed one together with that crank press, it was spot on timing wise and I just had to spread the lobes a little to get rid of the 0.003" initial run out.

That's almost the perfect scenario... I'd rather squeeze it to spec but, I'd be TOTALLY OK with spreading it, in-order to hit the mark. Lol.
Good job man!

 

[srcarr52]

That's almost the perfect scenario... I'd rather squeeze it to spec but, I'd be TOTALLY OK with spreading it, in-order to hit the mark. Lol.
Good job man!

Thanks.

Generally when squeezing them together you slightly tweak things such that the counter weight side needs to be spread a little to get the ends to runout straight, it was the right width but it just needed the press fits to be relieved a little on the meaty side.

 

[legdelimber]

I somewhat recall a magazine article about taking a 70's era 500cc Yamaha 4 stroke out to 601cc. Bored and stroked of course.
I believe that they used tungsten plugs in the crank weights for balance.

On the vibration? The writer said that the bike carburetor was set up right and bike ran just fine when riding it.
But yet when they strapped the bike onto a chassis dyno, they had problems with vibration and the carb went wonky and the engine just fell flat below mid-range revs.
They figured the vibration was frothing the fuel and thus causing the problem while strapped in.
There was no mention of dyno testing the engine, out of frame.

I've googled for the story but had no luck finding it.