Cretors popcorn engine

[black85vette]

Fortunately I have just started this build so I don't have much to catch up on.   It is my first shot at working with castings.  Kind of a mixed bag.   I like the looks of cast parts but as I look at them in the box  I kind of panic.   Where the heck are the reference surfaces?   Just a bunch of rough odd shaped pieces.   

For those not familiar with this engine, it is one of several models used on popcorn carts in the early 1900's.  Before electricity was available they used the heat from the boiler to pop the corn and the steam engine ran the stirring piece in the popper.

I was surprised how little turned up on a Google search.  Could not find any builds on forums and very few examples of replica casting kits done.   I found this one reference to a replica being bought and it shows some good shots of the engine:

http://modelsteam.myfreeforum.org/viewtopic.php?t=31984&start=0

So lets start with something I somewhat understand; the flywheel.   It is 8.5" dia and is the largest I have worked on so far.  Still nothing smooth or flat but at least I can grip it on the larger side of the hub then use a dial indicator to get the spokes running in the same plane.   Drill a small spot on the outboard side of the hub so a live center can hold it steady.   Then clean up the smaller hub and one side.   Flip it over and grip it by the smaller hub and use the first side as a reference to get it squared up.   The larger hub gets cleaned up and drilled for the live center also.   The second side of the rim followed along with the outside edge.


IMG_5519 by black85vette, on Flickr



IMG_5521 by black85vette, on Flickr



IMG_5533 by black85vette, on Flickr

I will set the flywheel aside for now.   It will require a great deal of clean up on the spokes.

[black85vette]

The next piece looks to be the most critical of the build.   The crosshead guide has to be centered and lined up perfectly with the cylinder / piston / head / piston rod.   I started by staring at it on the table.   It didn't help.  Finally decided the two longest sides were my best hope for a starting place and then reference them for the rest of the operations.



IMG_5534 by black85vette, on Flickr


So I got them as straight as possible and made some very light cuts to clean them up.



IMG_5544 by black85vette, on Flickr


Using a block of aluminum I made a channel for the guide to sit in that would make the clean sides mount in a way that the block could be used to line up the guide for the next step which was boring.    (No, I was not bored with it)   Added a couple of clamps to hold the guide in place.



IMG_5539 by black85vette, on Flickr



A right angle place mounted the block and guide to the lathe compound slide.   Then I was able to get it squared up with a dial indicator.



IMG_5541 by black85vette, on Flickr


Needed to cut away some of the block and clamps to allow the boring bar through the first time.   After that the boring bar just cut away the aluminum.   The objective is to create an upper and lower rail with a .75" radius in each for the crosshead to travel in.


Got most of the boring work done today.   Took a very long time with the slow speeds and light cuts required to keep the chatter and singing down.   Actually it was more like humming because the lathe didn't know the words anyway.     Nice thing was that using the carriage feed on the lathe reduced the amount of cranking.   Figured I could just about read War and Peace and watch all episodes of Star Wars while this was going on.

I caught some video of it and will post it as soon as I get it uploaded.

[steamer]

Purdy flywheel!

And nice cross slide set up too!



Dave

[black85vette]

Went ahead and got the short video posted.   Used a commercial 1" boring bar with a carbide cutter mounted in it.  Why?  Because it was FREE from a friend of mine.   Bar had 4 flats on it so I used the 4 jaw chuck to hold it.

<a href="https://www.youtube.com/watch?v=7usrzrQBo2I" target="_blank">http://www.youtube.com/watch?v=7usrzrQBo2I</a>


Now for a question.  When I got most of the cut done I pulled the cutter and put a small radius in it thinking I could make some very light cleanup cuts.   Instead I got some serious ringing which show up as patterns in the surface.   No amount of speed / feed / depth changes would correct it.

So now what are my options to clean up the surface?

[Maryak]

Try wrapping the bar or the part with electrical insulation taper, might just dampen the harmonics.

Best Regards
Bob

[zeeprogrammer]

The finish on the flywheel is astounding. Nice!
8.5"! That's a sizable engine.

Ah! You posted the video while I was writing.
Can't answer your questions...but cool video!

[Bezalel]

What Zee said x2
 
can't wait to see the rest of it.   
 
Bez

[smfr]

Ooh, this looks like a fun build. Did you get the castings from Coles?

Not sure how to solve the ringing problem, but I'd try Bob's electrical tape suggestion, or anything to change the mass of the boring bar, like clamping bits of metal to it (if you have room).

Simon

[Bogstandard]

I doubt very much if the 'ringing' is coming from the boring bar, but from the component itself.

Either try to give some support to the unsupported bit of the casting where the bad finish marks are or very carefully wrap it in rags to absorb the vibrations that are being set up as you cut the part.
You need to change the frequency that the parts are resonating at.

John

[black85vette]

Thanks for the compliments.  I really like how this cast metal can take a polish.  Other than everything getting black powder all over, it works pretty nice.

@smfr; yes this is a casting set from Cole's.

@John; I am going to try to get some support under it.   The parts being cut are in the center and clamped tight by the blocks.     But since they are being held out of the end of the compound slide I think some additional support is called for.

When I get a good finish with the boring bar how should I go about honing it?

[Bogstandard]

Blacky (sorry, don't know your real name),

You shouldn't be honing, that is mainly for i/c engines, where the scratches in the bore caused by honing hold oil to assist with the running in.

You should be using a process called lapping, where you are polishing the internal surfaces of the bore using finer and finer grades of lapping compound (toothpaste is good for final lapping).

If you are US based, then copper adjustable laps are very easily and cheaply available in the correct sizes you require, if you are here in the UK, then you will have to come up with your own method of honing. I use a spot on size delrin bar and normal valve grinding paste for the preliminaries then ending up with something like jeweller's rouge for final polishing.

I am sure some of the other lads will give you their ideas and recipes for getting your bore spot on.

John

[black85vette]

John;

Thanks for the clarification in terms.   I still get machining terms mixed up.    Made a change in my profile to show name and location.   That should help.

I have seen shop made copper laps but not actually made one.   Will they work OK for interrupted cuts like this guide?

[steamer]

Might I suggest that you run a HSS bit, with much less radius ....and hopefully a positive rake...  That will reduce the cut pressure...then I think you will need to change your feed...perhaps increase it a bit, to change the dynamics of the system as John has suggested....You need to get past the resonance pattern...or it will go on for ever...

At round tool with two flats ground on it so that the cutting force is axial should help.   If that isn't clear, I'll sketch something up or take a picture of one of my tools....

Dave

[black85vette]

   Time for the happy dance.

Think this one is licked.  Did a couple of things.   JasonB had told me before to use a between centers boring bar for this.  But being the smart a$$ rookie I went with the boring bar I had been given.

Took the time tonight to make a 20 inch boring bar out of 1 inch round stock.  Then also took the time to get out a good piece of HSS and ground it with the angles and relief it needed and a smaller radius also.   Made a nice clean cut right out of the gate.   Made a couple more passes at smaller and smaller depth and ran it both directions for each depth.   It is feeling pretty good to me.

Now I need to finish boring the hole in the flange to 1.5" to mate up with the cylinder head and then a couple of light facing cuts on the flange while it is still lined up and in the jig.

Does not take much to make me happy.   One new tool and one less task to do.

Now to figure out the lapping (not honing) tool.   Think I will try making one and see how it goes.

[steamer]

Glad it's working out Rick!

Dave