SERCEFLYER

Well here it is: my first attemps at machining a small (049) compression ignition engine. This is the start of the crankcase.

SERCEFLYER

Like most of you here on this forum, I have a weakness for small ic engines. So, when I decided to try to build my own, I went for the tiny, cute Taig Micro Lathe II (4.5 in swing over bed). I've dubbed it my 1/2A lathe!!! I got it for my dad (and me) for Christmas, and we've been having a blast just learning the basics of machining. It's a lot tougher than it looks at first, but it really is satisfying being able to make parts to 1 or 2 thousandths of an inch. We're slowly getting better at it-- we only junked the 2 first attempts at the crankcase. So many little geometric problems to figure out.

I think I've been bitten by the lathe bug.... thanks to you guys on the forum. (Now another hobby to tug on my pocket!)

SERCEFLYER

The first photos shows the backplate, and the second is the start of the crankshaft (12L14 steel).

For the lathe guys: If you can see from the photo, the bottom of the backplate is conical due to the clearance angle on my 1/4 in boring knife. Is there any way to cut a square bottom without grinding a new boring tool?

Tim Wiltse-RCU

SUCKER!!!! A machinest and his money soon part is what I always say....well not really always as this was the first time I said it Anyways I love my lathe and I have no skill, I am waiting on my rotary table and 4 jaw chuck to get to me this week so I can start playing on my mill next. Keep the pictures and up dates coming. What plans are you using for the engine?

Later,
Tim

SERCEFLYER

Tim,

So true. I don't want to think about the number of Cox's and little diesels I could have bought with what I've spent. But, if I can produce even one semi-functional 049 diesel, I'll be happy.

The plans are for the ML Midge that can be found on [link=http://archive.dstc.edu.au/BDU/staff/ron/midge/]Ron Chernich's site[/link]. (You can order the plans from him.) This site is a must for anyone wanting to get into this sort of thing. And Ron is a great guy to learn from.

George

ajcoholic

My Feedback: (10)

The Taig is a light lathe and you have to remember take a few thou cut at a time.. no more! If it starts to chatter, then you are taking too much.

Also, dont be afraid to buy a large number of high speed steel tool bits, a grinder and make your own bits, boring, cutting, parting, etc. The whole key to machining is having a good selection of bits you make up for a specific task.

The best is yet to come... Just wait untill you get it looking more like an engine... and the excitement builds!! My favourite part is when the last few bits and pieces are done and you assemble it all together.

Keep at at!

AJC

BMatthews

Resistance is futile.... you will be assimilated....

BHWAAHAHAHAHAHAHAHAHA... hahahaha... *cough, cough*.... man, I gotta stop DOING that... *cough*

For the backplate you need a special ground cutter. You want a perfectly square cutter with proper cutting relief angles in the end and on the one side. The side cut relief should be ground with a radius on the lower area that is tighter than the smallest cut you want to make. Leave the top flat and use it for light cuts at slightly lower speeds only. A fair number of HSS cutter blanks and a good grinder are your best friend for stuff like this. Smaller sizes for these specials reduces the amount of metal to be ground away. For example my machine uses 1/2 inch sq cutters for the most part but for these special one off's I use either 5/16 or 3/8 bits.

For a beginner that stuff is looking pretty good from here.

AndyW

My Feedback: (1)

Looks good from here. Soon you'll be chopping aluminum and steel more than balsa. Yes, the Taig is light and you need to take a bit of care but it's amazing what you can accomplish. As Andrew says, lots of bits, custom ground, will take you far.

My best investment with the Taig equipment was the milling attachment. Again, it has its limitations but there IS a lot that can be accomplished.

Pictured is my selection of boring bits. The middle two are from Taig. You ought to be able to get a flat bore bottom by advancing the carriage very slightly when you're at the max diameter of the bore. Then, reverse cut to the center. You have to be very careful and not take too deep a cut but with multiple passes, you can get a very nice, smooth flat to the bottom of your bore.

SERCEFLYER

This is all we got done tonight in the micro metal shop. We drilled the end of the crankshaft and tapped the hole with 6-32 threads. And then we set the taper angle to 5 deg and turned the end of the shaft.

This was my first attempt at tapping. The hole was drilled 0.500 deep. While tapping, I didn't feel much resistance until the tap was almost half way in the hole. There's a chamfer at the end of the tap, I think.

What's the rule on how deep to drill when using a chamfered tap? Hopefully, we cut just enough threads to hold the spinner bolt.

SERCEFLYER

This is what the partial crankcase looks like after turning the taper. Now the next step is to part off (part a bit, then grab a hack saw) and then chuck the parted end eccentrically in the 4-jaw chuck and try to turn a tiny crank pin. So far we haven't junked this piece-- we'll see tomorrow. I'm a lttle stressed just thinking about.

And, thanks about the advice on the square bottom boring-- will do that next time. (For now, I'll accept the interior cone as a cosmetic addition to my ML Midge 049-- only the outside surface touches the crankcase.)

AndyW

My Feedback: (1)

Looking good so far. My only concern is that your taper might be too shallow. If so, when you mount your prop, and the drive washer rides up on the shaft, with too shallow a taper, you may not ever be able to get the *@$# thing off. Ask how I know. Take your cue from the tapered collar on the early Norvels if you have one.

BMatthews

Ah, tapers. You're getting into the self locking angle. Different metals in contact all have an angle where they will self lock based on the coefficient of friction between the two. For example the angle of the Morse taper is well under the critical angle so it grabs and needs a forceful blow to unseat it. But a 15 degree taper will self center without locking so when the pressure is off you can easily lift it away. Serceflyer, your taper looks quite sharp. I think Andy is right and you're in for a lot of grief with the prop driver. I've seen a number of the smaller engines that sure look like they use a 30 degree included angle. And what do you know? A center drill is just what you need to "ream" the hole to that exact angle in the prop driver... Coincidence? Methinks not.

Finding bottoming or even middle taps for small sizes is not easy. Make your own by cutting taper taps down so you can clean out the threads after starting with a taper tap. The Dremel cutoff wheel makes short work of the job.

BTW, I'm an idiot... Here I am telling you to get smaller cutting bits for the special stuff and not realizing that you're already using 1/4 sq bits. Just get a bunch more and grind away to your heart's content.

BMatthews

I found a chart once on the web that gave the critical self lock angles between various metals but now I can't. I think it must have been listed under another name so I'm not using the right search words.

AndyW

My Feedback: (1)

I've got a PAW .06 with a prop drive washer that's tapered to suit the taper on the crankshaft. Can't recall the taper angle exactly but it was such that as you screwed the prop on, the drive washer drove back, further and further till it bottomed out against the face of the crankcase, locking up the whole mess. At no point did you feel you reached the limit with the feel of the wrench. Don't know if it was the softness of the prop drive washer that allowed it to simply keep expanding, or the taper, but you can get in trouble here to easily. [:-]

The other place I had trouble was with an MP Jets crank stuffed into a Norvel case. I didn't have front end components so I made my own split tapered collar from brass and prop drive washer from ally. I eyeballed the taper without consulting established practice and when it came time to take the engine apart, not heat, cursing, pleading nor threatening, would budge that drive washer. I had to destroy it with a chisel to get it off. Now I routinely use Neverseez just in case. Never slips and the assembly still comes off easily.

AndyW

My Feedback: (1)

BTW,

PAW on the left, Norvel on the right.

Also, where did you get the protractor? Been eyeballing angles too long,,, gettin' crosseyed. [sm=stupid.gif]

ajcoholic

My Feedback: (10)

Serce - my advice? Just follow the drawings! Guys, dont get too much into the small details such as tapers, etc with different metals or you are going to scare the poor guy away!

Especially for your first shot at this FOLLOW THE PLANS 100% and you wont go wrong.

AJC

SERCEFLYER

First, thanks a lot for the help. The machinist groups are great for basic shop practice stuff, but you guys know how to make a hunk of machined aluminum and steel fly!

About the taper at the end of the crankshaft: the drawings show that taper fitting into the equally tapered bore of the prop driver-- 10 degrees. Honestly, I don't really understand the reason for the taper. Once my batteries are recharged, I'll post a diagram to explain. Maybe you guys can figure it out.

Andy W.- I got the protractor from Harbor Freight-- it fits perfectly on top of the cross-slide, and it's accurate to less than .5 degree. Just set the angle on the protractor and move the compound slide until it matches.

AndyW

My Feedback: (1)

The reason for the taper? It's to keep the prop and prop drive washer from rotating when starting/running the engine. Some engines use a straight shaft but have a flat milled on one side and the drive washer has similar internal dimensions to suit to "key" the drive washer.

Pictured is the prop driver from the current Norvels and also the tapered, brass collar from the Jets.

But, Andrew is exactly right, best to follow the plans, (if all else fails ) And, a quick check of the taper on the Jets shows it to be 10 degrees. or so. Certainly not 15 but you know, now that I think of it, without Neverseez, it's still a bear to get off.

Anyhow, get those batteries charged and show us more!!

SERCEFLYER

OK, here's the detail on the taper fit between the end of the crankshaft and the prop driver. What's going on here?

AndyW

My Feedback: (1)

Serceflyer,

Could be my eyes and photo distortion, but a check with my dollar store protractor, against your picture shows your taper to be something like six degrees. If ten is called for, you may have an issue here.

AndyW

My Feedback: (1)

Well, my eyes and my cheap protractor weren't lying. The plans show 6 degrees. You mentioned ten. Did the instructions call for ten degrees?

SERCEFLYER

Looks like I junked the crankshaft—do not do it this way. It took a while, but I was able to chuck it eccentrically in order to turn the little crank pin. I was off to a good start, but right when I started making fuller cuts, the piece moved in the jaws!!! #%$%#$#@ !!!

Here’s the problem: there isn’t enough of the crank-web to chuck. The jaws wouldn’t reach the actual shaft, so I tried (unsuccessfully) to chuck just a small amount of the web.

I would have turned the crank pin first, but then how would I be able to chuck the piece and turn the shaft?

Part of the fun of playing with a lathe is coming up with solutions to these sorts of problems. It’s great when you can solve the problem, but this time I need some help. What am I missing here?

SERCEFLYER

Andy W.,

Here’s the detail on taper angle. You are right—the actual angle of the taper (from the lathe axis) is 5 degrees. (My protractor is set at 85 degress for the outside angle, so I think I had the compond slide set right to achieve the 10 degree angle as on the drawings.)

ajcoholic

My Feedback: (10)

Here is how I machine the crankpin.

First off, once you get an important thing like the crank bearing journal finished DO NOT EVER grab it with the steel chuck jaws. You will deform or mark it and it will be junk.

Get a small aluminum round, say about 1.5" diameter and a few inches long. chuck it in the 4 jaw chuck, off center the same amount as the crank pin offset. Bore a hole the same diameter as the crank bearing diameter.

Now, drill a hole for a setscrew that will enter the hole you bored, and drill and tap for a 1/4-20 setscrew. chuck this fixture in the 3 jaw and yoour hole will be offset the exact amount that the crankpin needs to be. Put the crank into the hole, USE A PIECE OF BRASS between the crank and the setscrew and tighten it to hold the shaft. USE THE TAIL STOCK CENTER to support the other end and now turn the crankpin. Go VERY slowly as it is a bear to machine on a small lathe but it can be done.

All my fixtures are at the shop, while I am home for lunch. I will take some pics and post later if my description did not make sense...

AJC

SERCEFLYER

AJC,

It's not totally clear to me-- I'll try to draw a sketch of what you've described. But, if you can get a photo or a a quick diagram, that would be great.

I'm a bit embarrassed that I tried to turn the crank pin this way. Seems obvious now that it wouldn't work.

Thanks.