Need Help!- Reference Flat for Scraping Dovetails

[Ed from NY]

Hi,

I need a reference for scraping the dovetails on my bench mill.

My Y axis has some play, but the real problem is that when the table goes from one side to another the play allows the table to resettle in a different position. That messes up any attempt to control Z, by as much as 0.010" end to end, with a discontinuity in the middle.

See video towards the end. The video is part of a series on my tribulations fly cutting, but it highlighted the Y-axis problem.

YouTube - Help me fix my Mill - Part 10.5 - Fly Cutting Steel

YouTube - Help me fix my Mill - Part 10.5 - Fly Cutting Steel

Anyway, I have tried it the wrong way with no references and make shift references. Different levels of success. It did not get me where I need to be.

Next step (or perhaps what the first step should have been) is to get some way to compare the dovetail at different heights to a reference. I need to do that on the saddle and on the machine base itself.

I'll probably need to buy everything because the closest thing I have to a reference is a machinist's square, but it is only 5" long and has a beveled edge. I need at least 8", more would be better as it could be useful in a different project.

Don't have anything I can use to shim it either... I was thinking a cheap set of parallels, but those are only rated in height, not thickness.

The dovetail angle is a bit less than 60, probably around 56 degrees (?).

Ideas of what I can get without spending much? What do you use?

Thanks!

[BillTodd]

It's not a great idea to use a boring head to fly-cut, the geometry of the tool is wrong and they are not particularly rigid, especially if that mill is turning as fast as it seem to be! The reason the tool digs in like that is because the cutting force will tend to cause the tip of a tool to bend down towards the work. The problem with a boring bar is that the length of the bar adds leverage to the tool exacerbating the problem.

If you have to use the boring head, use the shortest tool bar have - or make a very short bar for it.

As for scraping your dovetails, That's a lot of work, so you really need to make sure every thing else is checked before you start. Check the gib adjustments - are they too loose? Is everything well lubricated and clean etc. etc.

[Ed from NY]

Thanks Bill,

I contacted Criterion a couple of days ago on this particular application and I'm waiting to hear from them.

You can not see in that video but there is a very small transition on the previous fly cutting row in that same exact X position. That is seen as a change in the light reflection pattern. The difference in height between the second and first row also slightly increases as you go left. Plus the drop agrees with the Y position where the saddle was looser. I also have additional data on surfacing with end mills. All these things are pointing towards it being the table resettling.

Yeap, I did cover all the basics.

I know that mill intimately piece by piece by now. I can take it apart and put it together on muscle memory almost and adjusting the gibs is as familiar as drinking coffee by now

I understand the risks and the amount of work, but need to shape those dovetails

I have been working on one surface and I can get very close just with machinist's blue. But I want to be able to check it against a reference in case deviations in the base are giving me a bit of a false reading on the saddle dovetails scratch patterns.

Plus it would be nice to benefit from people's experience fitting machines

[Ed from NY]

Well I think I have passed the point of using references. Very close now. A few more sessions may be. Just scrapping minute amounts of material and I can do that with blue.

It is probably taking me a lot longer than it would have taken someone that is used to do it, but I'm happy to say it is pretty much in the bag.

Thanks!