I have been hurting my brain a bit more, thinking how to make this drag out a bit rather than wham, bam, that's it.
There are so few components in this engine I can do a lot of piccies to cover everything.
So I have decided to turn it into a little bit of an instructional build, showing newbies, in not too technical terms, how I achieve what I do.
But please bear in mind that this is the way I do it, someone else might do it an easier and better way, it is what I am happy with.
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The rotor is done and dusted.
The next major part is the outer casing. No drawings for this because it is rather easy to remember, there are only two dimensions for the block. Each side is 1 3/4" wide by 2" long.
Here is the raw block of ali, rough cut on the bandsaw out of a much bigger lump. It is about 1/4" oversize in all directions. What I am going to be doing is turning this rough block into a precisely sized block with all faces square and parallel to each other. This technique can also be used for getting square out of round with the same results.
When starting work like this ALWAYS check your fixed vice jaw for running parallel to the spindle cut.
I do it by putting a good solid parallel into the vice, set up a DTI to run against the parallel (you could use a normal dial indicator with a plunger if you can get it in). Tweak up the vice holding bolts, enough to stop it moving about, but with a slight tap the vice can be moved.
Position the DTI in the position as shown and wind the Y axis (back and forwards handle) until the DTI starts to register a reading. Reset the rotating dial to the zero position and then wind the X axis (side to side handle) so that the DTI is run along the face of the parallel. If the pointer starts to go anticlockwise, tap the left hand side of the vice near the tightening handle with a soft hammer until the pointer moves to the zero position. Return the DTI to the start position, re zero the dial and try again. If the pointer on the dial goes clockwise as you move right to left, the right side of the vice needs a tap.
Just keep doing this until you get no or very little movement on the needle while you track the full length of the parallel. Tighten up on the hold down bolts and recheck. If it still runs with no deflection, your vice is set up to perfection.
I always do this check whenever I start a job. No need to slacken of, just pop a para into the vice and do a quick check with a DTI. Tweak if needed.
The above didn't really need to be done with this job, as it is all flycutting top face work, but it is always nice to see how it is done.
Anyway, back to making something.
Pop the hunk of metal into the vice with one of the side faces upwards (the ends are done later), and rest it on a couple of matched para's. Tighten up. Nothing spectacular, just so that we can face the first side.
This pic shows what is needed. A flycutter (not essential, but for big faces like this it is an advantage). A nice dead blow soft hammer for tapping the job down onto para's, and a bit of lube for helping the cutting along. Ali can be a bit of a dog to get a good mirror like finish, so razor sharp tooling and lubricant are the right things to use. For ali, paraffin is the recommended cutting fluid, WD40 is now starting to be recommended as well. Because it is so expensive to use willy nilly, I always make up my own cutting fluid. It is white spirits with about 5% 3in1 oil, and I find it works really well. Dab it on the job when needed, whilst keeping well away from the spinning cutter.
This is what the profile of my flycutter is like, it was shown to me a long time ago and I use this shape all the time, it works in the same way as a round nosed turning tool to produce mirror like finishes. On ali, and a nice rigid machine, 0.100" (100 thou or 2.5mm) can be hacked off in one go, not recommended for beginners to do, but it is there if needed. On a job like this I tend to stick with 50 thou and below. Most people use a more standard straight edged bit in their flycutter. As I said before, I do it the way I am used to.
Back to the job in hand, take a facing cut across the top until all the old cutting marks are gone, then put a very fine cut of say 1 or 2 thou, with some cutting fluid in the mix and take a nice slow feed, fast cutter swipe across the face. You have cut your first datum face.
The first thing to do when it comes out of the vice after every operation, is fully deburr the part, and clean down around the vice jaws. One bit of swarf can knock all your faces out of square.
I am a great believer in marking things up, just so that I don't get confused between operations.
The face I have just machined is marked up D1, standing for datum face 1. I also mark on the end of the block where the datum face is.
Shown also is the most vital part of getting the bits square, a bit of soft round bar. I usually keep this in the channels on my miller table so it is always there, ready for use.
Now we set up for cutting the second side, to be square to the first. Datum face 1 goes towards the fixed vice jaw, the bit of round is put against the job and the vice is tightened up. Just do a rough tap down onto the para's (there is only rough faces against them still). Now do your cleanup and finishing cuts like was done on D1.
Datum 2 is marked up the same way as D1. These two faces should be totally square to each other.
Now mount the block into the vice as shown. D1 goes to the fixed jaw, D2 goes down onto the para's and rod inserted and vice tightened. Now is the time to gently tap D2 down onto the paras until both paras are just gripped.
Now you can machine the top face down to give the correct width of 1.750" between now D3 and D2. Take it down gently when getting close and do a finishing cut of a couple of thou. If you haven't got a mic to measure while still in the vice, the block can be taken out and measured any way you wish to get a reading. As long as the block is put back in the same position, and tapped down onto the paras you won't be far out.
If you have done it right, the faces D2 and D3 should be parallel to each other at the correct measurement and the corners between the datum faces should be totally square.
The bit of round bar is now no longer needed, there are three datum faces that are worked with.
The last datum to be cut goes against the fixed jaw, the first down onto the parallels. Tighten up and tap down. Take the last face down to the same setting as the previous facing cut (to 1.750" thickness). Fully deburr all around and check your sizes and squareness. You should be pleased with yourself if all sides are parallel and square.
I have set this shot up just to show how to get the ends square to the sides. This is the bit where the previous setting up with a DTI is needed, if the vice jaw doesn't run parallel to the cutting stroke you end up with off square ends.
Set the block down onto para's with a small amount protruding out of the end of the jaws (make sure the para's stay within the jaw area, otherwise you will end up cutting steel as well). You can then face across the ends to bring them to squareness and length (if you have a cutter long enough to reach from the top of the face to the bottom). I don't like this method because it usually gives a real crappy finish. There are other ways, like standing the ends up in the vice and flycutting the end faces, but the blocks have to be got perfectly vertical first. That is why I go over to the lathe for end finishing.
What I do is mount the job into my four jaw, it doesn't need to run true, near enough is good enough. Pack the jaws with the same type or softer material than the job. I normally use Pepsi Max cans cut up with scissors (If I tell Pepsi about this free advertising, do you think I will get some freebies). In this case I didn't have any to hand, so I used brass shimstock instead.
Face the end, then turn it A over T in the chuck and face and bring to length.
Job done, with one obvious mistake. Because I used brass instead of ali for protection pieces, I have a bruise mark on a nice clean face. It will easily be eradicated with a swipe across some very fine W & D, but it shouldn't have happened in the first place. Typical, always making extra work for myself, just by being lazy.
The next instructional bit will be how I bore the big hole in the end.
John
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