Building the Minimag

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NickG:
I'll be watching too. :thumbup:

Bogstandard:
Now the basic kit intro is out of the way, could I please ask the members, unless it is directly related to this build, not to post things like, 'I built one thirty years ago' etc etc, could you please leave that to the very end, after the build is completed, and we can then discuss it.
If there is a question about techniques or procedures then please ask, but again, as this is a testing build for a commercial product, and I am following a set of build instructions, please, again, no 'I would have done it this way' type posts. But if you are relatively inexperienced, and don't understand what I have done, then please ask, I don't mind explaining the why's and wherefor's. Plus I don't want to put anyone off from commenting, that is what posts are all about, but please try to keep them fairly short.

I expect this post to be linked to, and maybe become a 'running commentary' to the paper build instructions supplied with the kit. Hence I don't need it to be a long drawn out post. Except for my bits. :)

For the more experienced amongst you, I will be going thru the build showing how I do a few basic machining techniques, purely for people with lesser experience, so please excuse me if I show what you already know.

BTW, if you can build an engine that one of these are required on, I see no problems at all in you building one of these.

:ddb: :ddb: :ddb: :ddb: :ddb: :ddb: :ddb: :ddb: :ddb: :ddb:

So let's get on with it.

The very first thing is to assemble the supplied laminations. 32 pieces in each stack, one LH, one RH. After I put them together, I tightened up the screws and stuck a mic across them, just to make sure my count wasn't out, I came up with the same figure for both.
The nuts were then slackened off slightly, and a small bead of superglue run across the flat back side of the lams, in two places on each stack, between the screws. The glue wicked easily in between the parts, so things were quickly tightened up, wiped off the excess, and put them to one side. They will be used later in the build.

Whenever I come to do a new project on my machines, the first thing I do every time is get the machine ready to do a good job. If the machine isn't prepared, then expect crappy results.
The first job was to have a good clean up of the machine followed by a lube of all points. I am lucky in that I have one shot lube on my mill, but it is an important factor in getting precision. Oil forms a layer barrier between the metal working parts, it is that, if it is not there or 'topped up' can easily give you error of a couple of thou, so at the start of each working day, lube up.

The next part is getting you machine to cut straight, flat and square.
I go thru this routine religiously, even though not required.
With a DTI in my chuck, and a thick parallel in the vice, I sweep across the fixed jaw side from one side of the jaw to the other. If you don't have a parallel like this, and your vice fixed jaw face is in good condition, you could swipe along that.

It should read the same all the way across, if not, adjust the vice position until it is. Mine was still spot on, mainly because I have a bar on the bottom of my vice that locates into the table slot, and keeps it that way all the time. I just did this to show you what is required.

Next comes one of the most important bits, tramming the head. You might not think this is necessary, but without getting it spot on, what you think is a nice flycut flat surface just isn't, it will have a concave dippy down in the middle.

I made my own tramming tool, so it was laid on the table and the two gauges set to zero. You will have to find a way of doing your own tramming exercise if you haven't made one of these yet.

Tool now mounted into the spindle collet and brought down until at least one gauge reads zero. As you can see, my tram is out, not by far, but it needs putting right.

Swivelling the head a tiny amount soon had it spot on again.

Only last week, I was having a discussion with Stew about how a lot of people can achieve a nice flat face on the job, but just can't get it square to a face ajoining it. This is how I get faces square to each other when starting off with raw materials. I get everything square first, then bring them down to size.

Mark each end of the rough cut bar as shown. If bringing round to square, you machine the first flat and call it number 1, then carry on the same routine as this.

Put #1 side up, and if possible the bar sitting on parallels. No need to tap it down, just resting on them and tighten up the vice

Then using you sharpest cutter, just clean up the face until all rounded corners are gone.

Before going any further with cutting, the bar is removed and deburred straight away and the vice given a good clean down.

The now cleaned up #1 face is now put against the fixed jaw and #2 face sitting at the top, and again only gently resting on paras. Between the moveable jaws and the job, you put in a piece of soft round bar to take up any irregularities. The bar in this shot could have been a little lower, say half way between the para top and the top of the jaw, that will give a more even pressure onto the #1 face against the fixed jaw.

The #2 face is then smoothed off, ensuring you end up with a nice sharp corner with #1 face.

After the cleanup and deburr, #1 goes against the fixed jaw, #2 goes down onto the paras and the soft bar is put into position and the vice tightened. Now you can tap the job down onto the paras. NOT belting it down, but a very gentle tap with a soft hammer. I use a lead hammer, but hold it by the head rather than the handle, that way I am not continually bouncing the job off the paras by hitting it too hard. If you are lucky, and have the first two faces square to each other, both paras should be gently trapped under the job.
This puts #3 at the top, and again that is flatted off.

For the last side, the soft bar is no longer needed. Because #'s 2 & 3 are parallel to each other and both square to #1, then #1 is tapped down onto the paras.
#4 is now skimmed down to give the correct dimension on the job.

If extreme care is taken, and at the end only tiny cuts, you can get rather close to perfect dimension, this is about 2/10ths of a thou out. Close enough for me.

Then it is just a matter of bringing the other pair down to dimension, in this case, spot on.

Now comes the little matter of getting the ends square to the other four faces. If you have an end mill that will cover the whole depth then you can just set the bar onto paras, with the end sticking out of the jaws and then just face it off.
In this case, I stood the bar on end with it overhanging the vice jaws. By shining a light onto the background, you can see how far out of square it is.

By gently tapping the correct way, you can get it sitting perfectly upright.
It looks like it isn't quite there at the bottom, but it is, what you are seeing is stray light shining on the corner of the block.
Make sure the vice is tightened up fairly well, but not enough to do damage to the part.

Then a very gentle skim over the top until all the rough sawcut marks are gone.

Nice and square.

All that is done now is the face just cut is sat down onto paras and the opposite end is brought down to final length.

Again, almost spot on.

This block took me nearly 1.5 hours to get cleaned up and down to size, but we are not in a production environment where time is money, so I don't worry about how much time it takes.

All I am interested in, is that when I come to machine this block up, because it is well finished, I won't have any troubles getting everything else to be in their correct positions.

So the next thing will be, hacking this lump down to about half it's weight.

Bogs

madjackghengis:
Hi John, very nice and thorough entry into the project, hitting all the important parts for an accurate build. A very good start. :beer: cheers, mad jack

Bogstandard:
Many thanks Jack,

I had an hour on it this morning, and because I had taken the time to get it as best I could, I had no troubles setting it up and getting some cutting done.

The way it has been designed, now I am getting into it, I reckon if you can get somewhere close, and get the other bits to fit, then the final truing up will put things right.

It doesn't need to be made as accurately as I have done, but as I am working to drawings with no tolerances shown, I am doing my best to keep to those sizes.

John

Bogstandard:
A little bit more done today. It is time to start to cut bits out of the big ali lump.

Before I go into detail. Whenever I am cutting using a normal cutter, I very rarely attempt to do climb milling, sticking with conventional milling instead. My machine isn't geared up with the correct leadscrews to ensure it can be done safely, so I stay well clear of it normally.
There are plenty of descriptions about the difference between the two on the web, so if you are unsure about what I mean, then I would suggest you read and inwardly digest, to a point of where you think about it in your sleep. It could save your life one day.

On the build instructions, it says use the left hand top corner of the fixed jaw to set your basic 0,0 datum to. Unfortunately, I don't want to do that, purely because my vice doesn't support on the bottom of the job all the way to the outside of the jaw, on the KURT type, no problems on that score. So I will be moving my datum in towards the vice centre, and use my very rigid vice end stop as a substitute for the end of the jaw instead.

BTW, a few of the items I am showing have build posts for them on this site, vice back stop, tramming tool etc.

This is my setup, and it was an easy job with my edge finder to set up my datum corner.
I will just point out that the instructions do point to using a DRO for coordinate machining, but in my view, this magneto could easily be built plenty well enough by good layout and cutting to split the line.

In fact, even though I do have a DRO system, I still do a basic layout on a job such as this, purely as a double check as I am cutting.

Job mounted, pushed up to the backstop and gently tapped down onto paras, and the first cut on it's way.

On wide slots, or on any slot at all that needs to be accurate, I never use the correct width cutter to begin with. You will find that the cutter is usually flexed by the cutting forces involved, and will cut an oversized slot.

So in this case, a 16mm cutter run straight down the middle of where the slot is to be. It was taken down in stages until it was shy of full depth by 0.005". This is to allow a cleanup cut to be done at the very end.
Then I just gently crept sidewards to each marked line in turn.

As you get very close to the line, there are plenty of ways to measure to ensure you end up in the right place. On the finishing cut to the line, the tool was dropped to it's final depth and the cut was taken. The tool was then retracted up by 5 thou and the second line approached in the same manner.

Big slot in the right position, and to good size.

You then have to chew away at the two sides with the recommended 5/16" end mill. No problems in doing this, and it is at the same depth as the previous slot.
Except in my case, the marking fluid I used was washed away by the WD40 I use for cutting lube, and because my scribe lines were so feint, I overcut the length of the first slot by about 10 thou. But no problems, it isn't in a critical area and I just made the second one the same length, just to match it up.
None of us are perfect.

This is what you should end up with, minus ten thou on the rounded end.

The next bit is to lay a lamination against the slots just cut, and mark the 45 deg angled face onto the block. This is only a guide line, you fine tune as you cut it.

This bit had me perplexed for about thirty seconds.
The instructions suggest swivelling your vice by 45 degs either way to be able to machine to the lines. But as most people do, my swivelling base is languishing in the back of my shop somewhere, never to be seen again.

So I came up with this, a pair of V blocks, with both the blocks and the job being supported by the parallels. The cutter was already at the right depth, so it was just a matter of cutting the first one in the Y axis, and the second using the X axis.

Just like this, sneaking up on the angle so that the lam sits perfectly against all faces.

This is where the lamstacks will eventually be located. That is a job for next time.

A very boring day to follow. You will see.

Bogs

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