Getting the mill add on just right

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AdeV:
Bogs:

:bow:

As a newcomer to machining, I'm pretty much hanging on your every word, as these are all really interesting techniques and tricks your showing. Kudos. I sometimes have trouble keeping up with you, luckily not this time :thumbup:

Bernd asks why you use an end mill - same question, but also, any particular reason you milled on the X-axis? I'd have thought the Y axis would have needed fewer passes & hence been slightly quicker?

bogstandard:
I knew that this would come up and bite me on the bum.

It is all because I was in a rush and in bone idle mode.

My tram is very slightly out, and at this late stage of the game, I just didn't have the heart to have a good clean down and retram the head.

I will try to explain why I went the route I did.

Normally, when your tram is spot on, you will have no problems at all, and you would be able to use a flycutter to get a perfectly flat face.

But even with the tram being a minute amount out, you cannot get a perfectly flat surface in the X axis or an accurate angle cut in the Y.

So I used a normal end mill to give me what is in effect a flat surface made up of a series of ridges.

I have done a couple of C-o-C's to explain why I went the route I did.

I showed this the other day in a post about a problem someone was having. Showing what is happening when the tram of your machine is out in the X axis. Most people won't have the facility to tram in the Y axis.

These are the exaggerated effects of using a flycutter when the tram is out.

This is how you can simulate a flat surface by using a series of cuts with a smaller cutter. The top faces of the ridges form a very good approximation of a flat surface.

Don't let these pictures scare you into thinking that just a small bit out of tram is going to cause major problems. If the tram is out say by a couple of thou, the 'dishing' effect is minute.

The reason I have shown all this is that it could, under certain conditions, cause head scratching problems, and if you are aware of it, it can be allowed for.

There is a moral to all this.

Keep your tram spot on, and don't get caught using an out of tram machine.

Head bowed in shame Bogs.

bogstandard:
And now to answer Bernd's question.

If you have a look at the dovetail pictures in this post

http://madmodder.net/index.php?topic=2058.0

It showed the right hand dovetail in full contact with the top face and the left hand one just about on there, but still safe.

The reason for the thick gibs was twofold, correct the out of angle, but also to move the RH casting dovetail across some, so allowing more contact on the LH one. In fact they are now sitting equally on either side of the machine dovetail.

I hope this has explained sufficiently.

Bogs

Bernd:
Bog's

Ok, I understand your use of an endmill there. Makes perfect sense. And you don't have to hang your head inshame. We now know the reason why it was done.

I thought I had seen pictures of you showing the unit mounted. I thought it was in this thread. Now fully understand why they are that thick. I had thought I'd seen pics of a much closer fit, but my old mind is palying tricks on me.

Thanks for the nice explanation.

Now get that shop cleaned up and let us see what your next project is going to be. :dremel:

Bernd

bogstandard:
Thanks Berndt.

I forgot to answer this

--- Quote ---I'd have thought the Y axis would have needed fewer passes & hence been slightly quicker?
--- End quote ---

You are quite correct, it would have been slightly quicker, but exactly the same surface area needed to be cut. I have a tendency to cut from right to left. It is just a thing I do, and by doing it the same most of the time, I don't fall into the climb milling trap. I start at the far side and work towards myself.

I then don't overtax my brain cell too much, one less thing to worry about.

Bogs

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