Author Topic: Ohrndorf 5 Cylinder Radial  (Read 19301 times)

Offline Admiral_dk

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Re: Ohrndorf 5 Cylinder Radial
« Reply #60 on: February 10, 2021, 11:23:33 AM »
Congratulations on a very important part made, to a high degree of accuracy  :ThumbsUp:

I do not see what holds the gear for the camshaft i place - key or ?

Best wishes

Per

Offline petertha

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Re: Ohrndorf 5 Cylinder Radial
« Reply #61 on: February 11, 2021, 01:12:47 AM »
Hi Per. The designer recommends high strength retaining fluid (Loctite) for the gears. So the spur gear ID on the crankshaft OD (where there is very little hub meat left for a key anyways). The ring gear OD on the cam plate part. And the face to face mate surface between the 2 idler gears. I'm a little concerned by the last one. I may silver solder those. But holding off until it comes to clocking the timing. I'll determine which are the better gears to lock & which can be allowed to move into position.

I was a bit apprehensive about 'glue' but I've also seen many example where cam lobes & such were attached this way. I actually don't know what kind of forces are involved on the planetary gears, their sole purpose is to lift the valve rockers against spring pressure.

Offline petertha

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Re: Ohrndorf 5 Cylinder Radial
« Reply #62 on: October 11, 2021, 02:57:19 AM »
Sorry for the long lapse again. I will now continue on with the cam drive assembly. The O5 is similar to other radial engine layouts where the crankshaft drives a planetary gear reduction assembly, the output of which is connected to two separate cam plates. One plate is dedicated to intake, the other to exhaust where cylindrical cam lifters ride along the cam profile. As the cam lobe raises the lifter, the connected pushrod act on the rocker arms to open the valves.

The O5 planetary gear is a 4:1 reduction ratio. A 15-tooth module-1 crankshaft gear drives a 15-tooth intermediary gear which is sandwiched against a 10-tooth gear, which drives a 40-tooth internal (ring) gear. The intermediary 15/10 tooth gear cluster rotate together on an idler shaft. Because of 4:1 ratio, each cam plate has 2 identical lobes 180-deg apart for 2 corresponding events per single cam revolution. The intake & exhaust cam plates are phased angularly to each to achieve timing relative to TDC. Both plates are attached to a cup which contains the ring gear. Here are some overview sketches. Hopefully this will make more sense as the parts & assembly are shown in real life.

Offline petertha

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Re: Ohrndorf 5 Cylinder Radial
« Reply #63 on: October 11, 2021, 03:00:15 AM »
The gear plate is made from 2024 aluminum. It houses one of the 4 crankshaft bearings on the rear side & also holds the idler gear shaft on the front, nose case side. The plate attaches flush to the crankcase front face retained with M3 screws & also snugly fits the crankcase ID with a matching boss. The plans called for 1.5mm OD O-ring seal on the internal boss & another on the lip OD to seal the nose case.

I mentioned earlier that the original O5 design called for the nose case chamber to be partially filled with oil to splash lubricate the gear & cam assembly. The O-rings are to seal this bath oil from the crankcase & the outside world. But I was becoming less comfortable with potential oil migration issues & dragged my feet on this matter for as long as possible. For example, even though the rear bearing was presumably left shielded I thought oil would eventually get in behind the shield, dilute the grease & ultimately leak into the crankcase. Then the risk becomes hydraulic lock on lower cylinders. Also, because the lower cam lifter bushings would always be submerged in oil, it seemed like another potential migration path out.

So, after a lot of deliberation, I finally decided to abandon the oil bath mode. Rather, I made a series of modifications to my existing parts & this gear plate was one of them. Therefore, you will see a mashup of old & new pictures, hopefully itís not too confusing. I decided to subsequently drill an array of passage holes in the front plate to allow intake mist charge originating from the rear via the carb & crankcase, into the nose case & lubricate the gears & cams that way. This is actually the established lubrication method of other commercial & shop made radial methanol glow engines, so hopefully will prove to be the right decision. For added insurance I will make a threaded/capped port hole on the nose case to squirt lubrication oil in prior to running. I'll be careful during break-in runs to see how wet things are. The O-rings are already done & will still serve their intended purpose.

Offline petertha

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Re: Ohrndorf 5 Cylinder Radial
« Reply #64 on: October 11, 2021, 03:03:36 AM »
The basic gear plate profile was turned from solid bar. The main diameters & bearing counterbore were done in one setting. The O-ring groove dimensions also need to be done at this point before removing the part. The grooves were a bit fiddly to obtain the right fit to the matching components. Iíve seen some O-ring groove formulas that get you pretty close, but in the end, it was a progressive trial & error thing. I used 70 durometer Viton O-ring cord & spliced a custom ring using CA glue. That part went amazingly well. If you ever need oddball O-ring diameters to make, I can recommend this as a cost-effective alternative.

Offline petertha

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Re: Ohrndorf 5 Cylinder Radial
« Reply #65 on: October 11, 2021, 03:06:32 AM »
Pictures showing the stock gear plate design confirming fit to crankcase.

Offline petertha

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Re: Ohrndorf 5 Cylinder Radial
« Reply #66 on: October 11, 2021, 03:08:22 AM »
Once the plate was machined, it was set up in rotary table for hole drilling. I trusted the CAD pitch circle calculation to drill & ream the idler shaft hole using mill DRO.

Offline petertha

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Re: Ohrndorf 5 Cylinder Radial
« Reply #67 on: October 11, 2021, 03:10:09 AM »
Then I made an MDF fixture to hold the plate, return to lathe & counterbore the relief for idler bearing spur gear.

Offline petertha

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Re: Ohrndorf 5 Cylinder Radial
« Reply #68 on: October 11, 2021, 03:12:31 AM »
Here are some pictures of the subsequent plate modifications to drill the array of oil mist holes. Of course, that required a new fixture to reestablish the geometry which would have been SO much easier the first go-round. I managed to get the 2 lower apertures slightly intersecting the gear cluster so hoping it will get directly misted.

Offline Admiral_dk

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Re: Ohrndorf 5 Cylinder Radial
« Reply #69 on: October 11, 2021, 11:51:14 AM »
I think that there is a very good chance that you will be very happy with you desicion to use mist lubrication  :cheers:

Offline petertha

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Re: Ohrndorf 5 Cylinder Radial
« Reply #70 on: October 11, 2021, 05:15:59 PM »
I purchased the steel module-1 spur gears from Maedler, the same company I got the internal gear from https://www.maedler.de/
Originally, I contemplated making the spur gears myself. But these were reasonably priced, high quality & each gear requires quite a bit of modification. At my snailís pace construction, this was probably a good decision in hindsight. 

For the crankshaft gear, I first machined a closefitting aluminum pot chuck in the lathe. Then swabbed the ID surface with acetone. Then without disturbing this setting, inserted the gear blank which was as a tight push fit on the teeth & back face. Checked the bore with a DTI, all good. Then I spotted some CA in glue among the teeth to prevent it rotating loose & a spritz of kicker. Then bored out the ID to fit the crankshaft diameter & faced/profiled to length. The steel was reasonably hard but machined well. The glue held things firm, even during interrupted tooth cuts.

Once the assembly was removed, my plan was to heat the assembly with light torch heat, expand the aluminum more, break down the glue & gear would drop out. It put up a bit more resistance than I expected but eventually parted ways with slight persuasion from a rod. The crankshaft OD was just a hair over diameter near the rear stop so a bit of lapping compound got the two-parts fitting snug. The gear will be permanently bonded with Loctite retainer.

Offline petertha

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Re: Ohrndorf 5 Cylinder Radial
« Reply #71 on: October 11, 2021, 05:24:04 PM »
The 15T idler gear blank was held in a 5C collet for opening up the bore & machining to length. The 10T gear was positioned on an axle fixture to turn down a portion of the gear which then fits inside the 15T bore. The inner 10T gear bore rides on an idler shaft. The gear cluster will be bonded together with Loctite retainer.

Offline petertha

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Re: Ohrndorf 5 Cylinder Radial
« Reply #72 on: October 11, 2021, 05:28:38 PM »
The gear idler shaft is made from 5mm O1 tool steel. The end has a M2.5 threaded hole for flathead screw that retains a brass end washer in position. Including some pictures of one of my (many) lapping trials. My experience with drill rod is that is always within the stated tolerance, but is often eccentric in cross section. So, the purpose of lapping here is to bring it to size with appropriate finish, but also make it circular section. Here I have a steel clamp with a thumb screw tightening nut. It holds a sacrificial aluminum lap, slit through & also some internal relief slots made with a jeweler blade in scroll saw. I have a selection of inexpensive (AliExpress/Ebay) diamond lapping compound of graduated grits. The method worked reasonably well. But I have subsequently come up with an easier, less messy tool which is now my go-to method. Iíll show that tool a bit later.

After lapping & parting off, I torch heated & oil quenched. Then into the toaster oven to tan brown. I discovered it is sufficiently hard because I discovered the countersink was a teeny bit shallow & had to grind it bit to deepen, because my HSS tool just rubbed it. All good, everything seems to run smooth.

Offline petertha

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Re: Ohrndorf 5 Cylinder Radial
« Reply #73 on: October 13, 2021, 04:35:08 AM »
Cam Plates. I only have limited hardening experience with O1 tool steel & that was confined to relatively simple parts using a torch. I donít have heat treating equipment, but I discovered a local fellow who does heat treating for knifemaker community. He has all the appropriate equipment & experience with the many flavors of air quench blade steels. Considering the work that would go into producing the cams & the form factor, I had visions of it distorting into a Pringle chip, or cracking across the internal holes. I figured successfully heat-treating knife blades would present a tougher challenge than my cam plates. So, I sourced the (Starrett brand) A2 from my local KBC dealer, choosing a bit thicker Imperial stock which had to be thinned to prescribed metric dimensions.

I made a simple aluminum fixture puck for the lathe with 2 threaded holes. After a facing the puck face true, the A2 stock was mounted with matching screw holes & brought to thickness. The ID was rough bored with annular cutter then finished with boring bar.

Offline petertha

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Re: Ohrndorf 5 Cylinder Radial
« Reply #74 on: October 13, 2021, 04:37:57 AM »
The cam outline was band sawed roughly to outline but leaving 2 sacrificial ears with the original screw holes, which now served second duty to secure the part to the mill fixture. The ears correspond to where the cam lobes will occur. The lobe profiles are identical shape between intake & exhaust cams, but the four M3 mounting holes are angularly phased different to each other to achieve proper timing. One plate has M3 clearance holes, the other plate holes are threaded. Therefore, the cams donít lend themselves to be stacked together to make both intake/exhaust plates simultaneously.

The rotary table was first zeroed to the quill center. Then the fixture assembly was positioned concentrically on the ID hole with DTI & also along an edge of rectangular jig plate. Now the M3 holes could be drilled as well as the array of larger holes. These holes were a bit of foresight on my part relating to the same possibility that mist lubrication might be in my future, because drilling these holes after the cams were hardened would be very difficult. So, I came up with a CAD pattern which I could also replicate on the ring gear cup which the plates mount to & this would allow mist lubrication to flow through from rear to front. I was a bit concerned these holes would be great places for the cam to crack during heat treating but it turned out OK. Actually, the plans called for larger holes & non-symmetric spacing so it was a bit of faith.

I used an endmill & rotary table to cut the main profile, which is the valve closed, non-action surface. Overall, it went according to plan. Just have to be careful about entering & exiting the cut accounting for RT direction & backlash. The lobe ramp profile shape was created by the radius defined by the EM diameter as per the plans.  You can see I have a small Sherline 4Ē RT clamped in my mill vise bolted to an intermediary plate held in my main 6Ē vise. I feel the RT was accurate enough but found myself doing light cuts because I could feel the cutting action on the handwheel. Next time I would use my larger RT which is a bit more solid.

 

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