4th axis options?

Kenre · Jul 4, 2020

Currently i manually machine 2 stroke engine liners in a Dividing head tilted to various angles for different ports. I set the angle for said port, wind the handle X amount of turns and degrees, move Z axis a few mm, turn handle back etc.

What options do i have for a tilting 4th axis for CNC? Would be used on a Robodrill.
I dont need anything large, parts are less than 2 inches long.
Ive never seen such a setup, is a 5 axis unit the only option?

Prices for 4 or 5 axis units are astronomical! I wouldnt be scared to build my own hardware, add suitable servos and drivers, depending on how difficult to integrate it.

EmGo · Jul 4, 2020

Kenre said:
Prices for 4 or 5 axis units are astronomical! I wouldnt be scared to build my own hardware, add suitable servos and drivers, depending on how difficult to integrate it.

I hesitate to offer this, since it's really a hobby-grade device (calling it a "machine" is a stretch) but for chamfering transfer ports in small engine liners, might work ... it's about $ 1,000 USD for a five-axis version. Maybe could even cut the ports totally, I dunno, you'd have to try.

View attachment 293255

You could probably improve it a lot just by replacing that aluminum crap with a steel weldment ....

Kenre · Jul 5, 2020

You could probably improve it a lot just by replacing that aluminum crap with a steel weldment ....

LOL, I built my own 3 axic cnc a few years ago, Mach 3 controlled, and it looks like a Tank compared to that!
At least mine was cast iron and steel. It got me started, now i need a real one hence the robodrill .

The liners are brass with the ports machined through the walls. Very tempted to Fab my own unit from a few blocks of cast iron.

Vancbiker · Jul 5, 2020

Kenre said:
......The liners are brass with the ports machined through the walls. .....

Liners from brass?? I'm curious, never saw a two stroke with a liner that was not cast iron. You said these were small is it a model engine?

Kenre · Jul 5, 2020

Hi Vancbiker,

Yes model engines for RC racing boats. 15cc capacity.
Liners are machined from brass with all port windows, then the ID is hard chromed and ground to size with a taper that gets smaller towards the top. Under operating conditions the top of the liner expands slightly with temperature. High silicon pistons are used with no rings.

I could possibly use a collet chuck to hold a mandrel to machine the ports. No need for a huge rotary table.

Vancbiker · Jul 5, 2020

Very cool. The hard chrome makes sense. I have seen 2 strokes where the entire cylinder is cast aluminum and the bore is plated or metal sprayed then sized. I'm guessing the cylinders have the transfer ports milled into the side of the bore and the sleeve is used to make one wall of the port then. Super nice. I'd love to see more.

Long ago I water cooled one of the Yamaha RD400 motorcycles I raced. Twin cylinder 400CC. Similar idea to your tapered bore, I only built the water jackets from the bottom of the exhaust port up. Then the cylinder retained it's as honed, straight diameter. Machined new heads from solid with water passages milled in. Used a waterpump gear driven off the end of the crankshaft and radiator from a Yamaha TZ350 race bike.

I recently picked up a couple of 5" thick blocks of 7050 aluminum at a low price. Dreams of machining crankcase halves for a 500CC twin using 250CC motocross cylinders and heads are swirling around in my head.

EmGo · Jul 6, 2020

Vancbiker said:
Dreams of machining crankcase halves for a 500CC twin using 250CC motocross cylinders and heads are swirling around in my head.

Go all the way - one liter square four !

Do you remember the kwacker roadracing twin with counter-rotating cranks, fore-and-aft cylinders and rotary valves ? That was one cool sumbitch

Milland · Jul 6, 2020

Vancbiker said:
Very cool. The hard chrome makes sense. I have seen 2 strokes where the entire cylinder is cast aluminum and the bore is plated or metal sprayed then sized. I'm guessing the cylinders have the transfer ports milled into the side of the bore and the sleeve is used to make one wall of the port then. Super nice. I'd love to see more.

Long ago I water cooled one of the Yamaha RD400 motorcycles I raced. Twin cylinder 400CC. Similar idea to your tapered bore, I only built the water jackets from the bottom of the exhaust port up. Then the cylinder retained it's as honed, straight diameter. Machined new heads from solid with water passages milled in. Used a waterpump gear driven off the end of the crankshaft and radiator from a Yamaha TZ350 race bike.

I recently picked up a couple of 5" thick blocks of 7050 aluminum at a low price. Dreams of machining crankcase halves for a 500CC twin using 250CC motocross cylinders and heads are swirling around in my head.

7050 is among my favorite Al's. Make sure you orient the rolling direction of the two blocks to be the same when mated. Won't make a huge difference in properties, but why not?...

Vancbiker · Jul 6, 2020

EmanuelGoldstein said:
Go all the way - one liter square four !

~200+ hp and a razor thin powerband. 30 years ago I'd have been good with that kind of fun. Less so now.

EmanuelGoldstein said:
Do you remember the kwacker roadracing twin with counter-rotating cranks, fore-and-aft cylinders and rotary valves ? That was one cool sumbitch

Yep, way cool design. Rotax copied it and made it available to folks for a few years. I know a guy with one in a shifter kart.

Vancbiker · Jul 6, 2020

Milland said:
7050 is among my favorite Al's. Make sure you orient the rolling direction of the two blocks to be the same when mated. Won't make a huge difference in properties, but why not?...

Yes it cuts so nice. Both blocks still have grain direction arrows visible. I was planning to keep aligned. Not so much from concern about mechanical properties but possibly thermal expansion. I've never researched it, but does grain direction affect dimensional growth? Another thing to ponder.

EmGo · Jul 6, 2020

Vancbiker said:
~200+ hp and a razor thin powerband. 30 years ago I'd have been good with that kind of fun. Less so now.

You don't have to tune for max power, ya know. You could go for 120 hp and have it pull like a Peterbilt. A fast Peterbilt

Vancbiker · Jul 6, 2020

EmanuelGoldstein said:
You don't have to tune for max power, ......

Ahhh, but the temptation......

Actually I have become a fan of the torque. After 40+ years of riding 2 stroke street bikes and transitioning to 4 cylinder 4 strokes, all with moderate torque but an awesome top end rush, I bought a twin. Same HP and peak torque as the last 4 cylinder bike, but torque is available now about 4k lower rpm than the 4 pot yet redline is the same. Lets one get a bit lazy with the left pedal.

Kenre · Jul 6, 2020

Vancbiker said:
Very cool. The hard chrome makes sense. I have seen 2 strokes where the entire cylinder is cast aluminum and the bore is plated or metal sprayed then sized. I'm guessing the cylinders have the transfer ports milled into the side of the bore and the sleeve is used to make one wall of the port then. Super nice. I'd love to see more.

Long ago I water cooled one of the Yamaha RD400 motorcycles I raced. Twin cylinder 400CC. Similar idea to your tapered bore, I only built the water jackets from the bottom of the exhaust port up. Then the cylinder retained it's as honed, straight diameter. Machined new heads from solid with water passages milled in. Used a waterpump gear driven off the end of the crankshaft and radiator from a Yamaha TZ350 race bike.

I recently picked up a couple of 5" thick blocks of 7050 aluminum at a low price. Dreams of machining crankcase halves for a 500CC twin using 250CC motocross cylinders and heads are swirling around in my head.

Yes the case has the ports cast into it. liner drops in from the top.

Very nice stuff to machine 7050. My cases are 356 T6. I cast them myself. Only part of the engine build i dont do is the heat treatment of cases, crank, conrod and drum induction valve.

Milland · Jul 6, 2020

Vancbiker said:
Yes it cuts so nice. Both blocks still have grain direction arrows visible. I was planning to keep aligned. Not so much from concern about mechanical properties but possibly thermal expansion. I've never researched it, but does grain direction affect dimensional growth? Another thing to ponder.

Did some quick searching, didn't find anything specific to CTE. I'll bet there's a very small effect, and for most purposes none. But if you feel like digging (but not Douging) some more here's a place to look: aluminum alloys: Topics by Science.gov

Vancbiker · Jul 6, 2020

Kenre said:
...... I cast them myself. Only part of the engine build i dont do is the heat treatment of cases, crank, conrod and drum induction valve.

Thanks for the pics. The more you write, the more impressed I get. Great work!

Milland said:
Did some quick searching, didn't find anything specific to CTE. I'll bet there's a very small effect, and for most purposes none. But if you feel like digging (but not Douging) some more here's a place to look: aluminum alloys: Topics by Science.gov

Thanks for having a look. One less thing to take into consideration.

Kenre · Jul 6, 2020

Thanks Vancbiker, You have been of great help to me stepping up to CNC.

The cast alloys have a little less thermal expansion than the wrought ones. Depending on bearing sizes you may have to take that into account for bearing fits.

I use a 4140 bearing housing that is shrink fitted and bolted into the case. Bearings and steel housing have similar expansion so i dont need heavy shrink fits like other engines. Also much more stable.
Engines run on 40 to 50% nitromethane, RPM from 22000 to 26000.

Any idea on this 4th axis? If i was to make a tilting table how difficult to get it working in a robodrill? Fanuc 16i. Servo, Servo driver?

BROTHERFRANK · Jul 6, 2020

Hey Ken. Did you get the Robo in?

Kenre · Jul 6, 2020

Hi Frank,
Its crated up waiting to be picked up from the machinery movers.
6 to 8 weeks before it arrives. Believe me every day i wait takes forever, i hate waiting!!
So looking forward to it!

Vancbiker · Jul 6, 2020

Kenre said:
Thanks Vancbiker, You have been of great help to me stepping up to CNC.

The cast alloys have a little less thermal expansion than the wrought ones. Depending on bearing sizes you may have to take that into account for bearing fits.

I use a 4140 bearing housing that is shrink fitted and bolted into the case. Bearings and steel housing have similar expansion so i dont need heavy shrink fits like other engines. Also much more stable.
Engines run on 40 to 50% nitromethane, RPM from 22000 to 26000.

Any idea on this 4th axis? If i was to make a tilting table how difficult to get it working in a robodrill? Fanuc 16i. Servo, Servo driver?

I know that some grades of cast have high silicon content to minimize thermal expansion. Casting is beyond what I can do so would have to stick with machined parts should I pull the trigger on trying to build an engine. When run hard the RD400 main bearings would slowly plow the anti-rotation nub through the lower case. I fixed that by fitting a dowel pin for the nub to stop against. Doubled the life of a set of cases doing that.

The last Robo I worked on was mid 80s so don't know anything about one as new as you are getting. The 16i can do full 4th and 5th, but very costly. A tilt rotary indexer would be less money, still not cheap though. For porting the liners it seems to me that would work well enough.

I'd have a look at Animatics SmartMotor product to see if they have something in an IP rated motor with RS-232 comms. I've used them in silicon wafer processing machines and they were easy to apply. The models we used would not have been suited for a wet environment. I've also used Yaskawa single axis drives. This was all long ago so don't know what the current offerings might be. I suspect that getting a drive that will accept RS-232 data for a position command may no longer be easy to get. I'd guess that most are using some kind of bus architecture. Probably best to discuss with a local automation supplier.

4th axis options?

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