Elmer's Kimble engine

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arnoldb:
:beer: Rob, thanks mate. I'm a wee bit slow on this one though :palm: - still a lot left to do.

Thanks John :beer: - :lol: it might be a tad small; there's some 10BA coming up soon as well... M6 is HUGE :lol: :lol:
(Rob very kindly sent me the 10BA taps and a die 2 years ago - must have been too small for him too... :lol: - Rob, Thanks mate :bow: - just joking! )

:beer: Cheers David. Sorry for puzzling you :palm: - but I'm glad you're getting it. I hope when I'm done with this one, it should be easy for anybody to understand :thumbup:

Thanks very much Dave :beer:

Got to the rotary valve today. The plans for the valve itself is a separate chapter in Elmer's book.
I went about making it quite differently from the way Elmer describes - in fact, I did not do a single bit of marking out...

As I'd made slight dimensional changes to the engine block in the valve area to suit my available reamers, I had to re-calculate some of the dimensions of the valve. Most importantly, it's slightly bigger at a close 10mm fit compared to the 3/8" (9.53mm) the plans call for. This meant that some of the porting cut-outs had to be slightly deeper than those shown on the plans - all by 0.235mm ~ 0.24mm. The 1/8" shaft section was re-sized to a running fit for 3mm.

First I turned down a bit of 1/2" brass rod. An 8mm long section 2.98 mm thick to match the 3mm reamed hole in the the back engine cover and the next section 9.99mm thick for a close fit in the reamed 10mm hole the engine top:

:ddb: I got a nice smooth finish just turning to size, so no lapping needed here.

Off to the mill with the dividing head mounted in the vise, and the edge finder and hand-wheel zero-rings used to locate things - from this point, all operations were done according to mill dial readings:

The valve needs a 1.6mm hole drilled accurately through it's center, but on one side, the hole is connected to a 2.4mm slot. Rather than have the drill bit wandering on a curved surface, I first milled the slot, and then drilled the hole - much easier this way:

Another small change to Elmer's design follows - this time to correct a booboo that crept in when I drilled the port holes in the engine top; the drill wandered a bit on both holes, and they are pretty far off axially compared to the valve center line. The original valve design uses just the 1.6mm through-hole to supply air to the ports in the engine top - meaning everything have to align pretty darn accurately, and I don't have that... So to compensate, I milled a short slot 1.6mm deep axially on the other side of the workpiece (rotated 180o since the last operation):

After milling the slot in the photo above with a 1.5mm cutter, I followed it with a 2mm cutter - which might be a mistake... I'll see if this is OK later.

The exhaust cut-outs followed - taking care to cut them both from the correct side; one had to be done feeding in on Y, and the other feeding out on Y:

Back to the lathe, and parting off - an action photo for a change:

The finished valve:

Well... not quite. Seeing as I have this one transparent engine cover, and one of the most difficult things to explain to people when they're looking at my little engines is always how and where the air or steam goes inside the invisible bits of the engine, I decided to add a cross-section of the valve cut-outs on the "visible" face of the valve. I just free-hand milled this lot with a 1.5mm cutter 0.1mm deep:

The 1.6mm drill bit sticking through there is what I used to estimate level and orientation when I clamped up the workpiece :lol:

With the milled out bits on the valve face coloured in with a permanent pen, it'll look like this in the engine top:

:beer:, Arnold

foozer:
Them pieces are getting kinda small, with my handful of thumbs, heh heh heh

Looking good

Robert

saw:
Wow :clap: :clap: :clap: :clap: :clap:

arnoldb:
Thanks Robert & Benni :beer:

Today's little bit, the eccentric. It's not a difficult part to make at all - in fact all the difficult bits of the engine are now done - but once again I made a slight change to it.
If made as per plans, the eccentric is bolted to the flywheel, and when the engine is assembled, the eccentric ring is retained between the flywheel and the bearing column.
I don't want the eccentric ring to touch the bearing column when the engine is done, simply because the column will be painted, and the ring will either rub off the paint, or the paint will add quite a bit of friction while running - or both.
So I decided to add a step to the eccentric and eccentric ring to prevent that. The ring will still run against the flywheel on one side, but that's OK, as the flywheel won't be painted.
I'm also going to make the eccentric ring a split assembly rather than one piece. This is mostly for ease of assembly; this engine will be finicky to assemble when done, so I'd rather do a bit of extra work up front. It will also add some visual appeal - I hope.

Started turning up the eccentric - a bit of 20mm silver steel turned down to 17.5mm, and a 1mm long step turned down to 16.5mm diameter:

Off to the mill and mounted on the rotary table - purely for the fact that it's easy to center the RT to the spindle, plonk the chuck on it and dial in the hole locations. The two holes needed drilled - the most important one is the 6mm hole on the right, as that determines the eccentric offset. The hole on the left is 2.5mm - that will be transferred to the flywheel and then drilled out to 3mm:

Back to the lathe with the chuck, and parting off at thickness:

It looks like the lathe is running hell-for-leather in that photo, but actually, it's only running at 110rpm - I can't do much faster than that on parting steel. The lathe's spindle bearings is a bit worn, and I have a load of backlash on the cross slide feed nut as well. To top that lot, the "parting" blade I'm using is actually a HSS wood plane cutter that I ground down, and anything faster than that on steel would just toast the cutting edge. Not to mention the fact that this was an interrupted parting cut because of the two holes in there :coffee:

Once parted off, I spent some time and energy to file away the tool marks on the parted face, thereafter a bit of rubbing on emery, and the parted side of the eccentric is all nice and shiny. Shoved a bit of 6mm silver steel through it and the flywheel, and clamped the lot together with a toolmaker's clamp, and then clamped the clamp in the mill vise and transferred the 2.5mm hole into the flywheel - taking care not to have the hole exit on the other side of the flywheel:

Off to the drill press, and with the same toolmaker's clamp trick, opened up the 2.5mm hole in the eccentric to 3mm, and countersunk it for a nice fit for some 3mm countersink screws I have:

Next I tapped the hole in the flywheel to M3, shortened one of the M3 countersink screws for a proper fit, and this is what it looks like assembled together:

:beer:, Arnold

DaveH:
Excellent Arnold :thumbup: :clap:

This is going to be a smasher :bow:
:beer:
DaveH

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