Mery Explosive Engine

[Chipmaster]

I saw a part built Mery Explosive model engine at a Model Engineer Exhibition possibly 20 years ago then more recently YouTube videos of completed engines running. The way the engines ran fascinated me so when a set of castings were for sale on eBay UK a couple of months ago I read all of the build articles I could find on the internet and took the plunge despite knowing there would be difficulties carrying out some aspects of the machining with my machine tools.

Here is the set of castings.

 The set of castings. by Andy, on Flickr

My first consideration was the 150 and 50 tooth gears. I reckoned it would be advisable to determine the position of the crank and countershafts after I had the two gears meshed together. I have no experience of cutting gears, the  B&S  type dividing head that was given to me is a bit doubtful and I would have to buy the appropriate gear cutters. Fortunately a local firm Redditch Gears quoted a reasonable price to cut the 150 teeth on the pre machined to 4.75" diameter iron casting and I was able to buy a 50 tooth 32 diametrical pitch, 20 degree pressure angle steel gear off the shelf from HPC Gears. Therefore Redditch Gears cut the 150 tooth 32 dp gear with matching 20 degree pressure angle.

The iron casting for the 150 tooth gear.

 Blank cast iron gear wheel. by Andy, on Flickr

Machining.

Machining the gear casting by Andy, on Flickr

Videos, click on the picture to open the Flickr website.

Machining the gear casting by Andy, on Flickr

Machining the gear casting by Andy, on Flickr

Ready for the teeth to be cut. The bore is 9/32".

Gear casting ready to have the teeth cut by a local gear cutting firm. by Andy, on Flickr

I was asked to provide a steel disc to support the delicate cast iron gear blank.

Steel disc to support the iron gear wheel by Andy, on Flickr

The steel disc was machined to be just a few thousandths below the root circle diameter of the iron gear wheel as can be seen with the edge of the casting projecting beneath the steel disc.

Steel disc to support the iron gear wheel by Andy, on Flickr

I dropped the casting and supporting steel disc in on a Monday and the gear was ready for me to collect two days later.

150 tooth gear cut by Redditch Gears. by Andy, on Flickr

Andy

[crueby]

Great start!  The castings look to be very good quality. Watching along...   

[Dave Otto]

Cool project Andy! Looking forward to following along.

My good friend Max built one of these a number of years back and it has always been a good runner. He added heavy counter weights to the crankshaft which really smoothes out the rocking motion when running. If I remember correctly he originally made a built up crank shaft with taper pins and loctite, the crank failed in short order. So after that he made a one piece crank for it. Some claim that a two into one exhaust is required for proper running but my friend's engine seems to run just fine with two individual stacks. It is also important to adjust the piston for equal compression on each end of the cylinder. If there is any interest I could get photos and maybe a video of his engine.

Dave

[Jasonb]

Will follow along as I too have always liked the Mery

[Jo]

 

Nice to see your set of Mery Castings seeing the light of day Andy 

They did a good job on that gear  I will be practising on a blank before I cut mine. There is nothing worse than getting a gear with a half tooth  I like their request for the two steel supports I will try to remember that 

Jo

[Jasonb]

It would be interesting to know what method they used to cut it, if a gear planer or shaper then the force against the gear would be more than hobbing or as we do it with involute cutters. A bit of MDF would be enough to support the casting for small 32DP Involute cutters Or just back up the far edge with a solid stop which I have done in the past.

PS Only one backing support Jo.

[Chipmaster]

Thanks for your comments folks.
Yes Crueby the castings are excellent and Dave, I would gratefully receive any advice your friend Max can give, photos and videos most welcome. There seems to be some gaps in the set of drawings or items I don't understand .
My early efforts at making model engines made me wary of fabricating crankshafts because a couple of my fabricated cranks failed, one when the engine backfired and the other went banana shape due to the heat of silver soldering. I then switched to carving crankshafts from solid flamecut profiles but that's a slow process. However, in recent years I have used silver solder to assemble a few crankshafts that have survived. 

Jo & Jason - I think Redditch Gears said they used a gear shaping machine (not a single point shaper) I'll ask them what method and machine they used when I next drive by.

Andy

[Chipmaster]

This is the engine's cast iron base or body, it's just like the trunk guide of a steam engine.

 IMG_8436 by Andy, on Flickr

To bore the trunk guide using my Chipmaster lathe I had to mount the casting on its side as other Mery builders had pictured in their builds on the Internet. Standing upright the casting's centreline was too high for the lathe. At last I had found a use for a piece of 1/2" thick steel plate that had been leaning against the wall in my garage for twenty years. If I removed the topslide and attached the steel plate to the cross slide I could mount the casting sideways on two angle plates.   

Tabs by Andy, on Flickr

To start the feet were milled flat. Relying on the the 3 machined stubs (white arrows) projecting above the casting as sold by Marti Models which were parallel to the horizontal centreline of the trunk guide. 

IMG_8482 by Andy, on Flickr

IMG_8479 by Andy, on Flickr

Four 1/4" clearance holes.

IMG_8516 by Andy, on Flickr

The casting was bolted on to a piece of gauge plate 3/8 x 4 x 18" (expensive) that would be essential for holding the casting for various machining sessions.

8518 by Andy, on Flickr

Steel plate bolted to the cross slide.

IMG_8529 by Andy, on Flickr

IMG_8530 by Andy, on Flickr

I spent a long time measuring and marking up the casting, I found some of the measurements in the drawings for the engine body to be either impossible or my casting was the wrong shape. Nothing insurmountable just perplexing. Anyway the casting is pictured below, securely held / rigid ready for boring the trunk guide section.

IMG_8533 by Andy, on Flickr

IMG_8534 by Andy, on Flickr

[Jo]

You are moving along really fast when we think about how long you have had these castings.

I see you have a taper turner on the back of your Chipmaster  I couldn't see a DRO read head 

Jo

[john mills]

methods of cutting gears what the cutting process is used what the cutting forces are .the fallows type shaper shaving the teeth or hobbing
John

[Jasonb]

I've had to resort to the sideways mounting method a few times.

Were you able to make use of the bridge between the bearing housings to mark and punch/drill the ctr line which would have helped with setting up.

[Chipswitheverything]

Very interesting photos of your set up and the machining on this quite delicate and difficult ( and rather precious ) casting.  It certainly justifies and needs the careful thought that you are giving to the preparation and methods in dealing with it.  Excellent!  This should be a fine engine.  Dave

[Chipmaster]

Hello Jo, a DRO for my Chipmaster lathe happens to be topical, have you got a taper turning attachment?

I am discussing with Colin whether it is feasible to fit a DRO due to the position of the taper turning attachment at the back of the cross slide. We know DROs have been fitted to Chipmasters without taper turning (TT) attachments. If the scale is positioned low to avoid the TT attachment it might partially block the openings in the bed where swarf falls through. I rarely use the taper turning attachment but I would have to have the non taper turning parts / assembly / replacements if I dispensed with it. However, it's an excellent accessory when you need it.

I would like to hear from anyone who has overcome this problem.
IMG_0125 by Andy, on Flickr

IMG_0126 by Andy, on Flickr

IMG_0127 by Andy, on Flickr

IMG_0128 by Andy, on Flickr

IMG_0129 by Andy, on Flickr

IMG_0130 by Andy, on Flickr

IMG_0131 by Andy, on Flickr

IMG_0133 by Andy, on Flickr

Andy

[Jo]

Yes Big C has both the original Colchester Taper turner and one of Coilin's DROs fitted 

Jo

[Chipmaster]

Hi Jason,
yes I did make use of the bridge between the bearing housings on the casting I filed a flat surface on the end and marked it simultaneously with all the other scribing on the casting. Doing that provided additional assurance that my measurements, marking and position on the lathe were correct. However, the proof will be whether the crankshaft is perpendicular to the cross head and I won't find that out for a while.

Hello Dave, yes indeed there's always that element of risk and excitement when working on these castings.

Andy