Dovetail Tolerance

[Baithog]

Nothing is ever exact. There is always some variation. A dovetail measuring 6.000000" at one end will not be 6.000000" at the other. How much can a dovetail member taper before it locks up? How much before it gets too sloppy for a hobby level slide?

I am still waiting for some of my tooling to start scraping the X-axis, so I started setting the y-axis up for machining. I'm an 1/8 of an inch or so short on Y travel on my mill/drill unless I take the DRO scale off. So, if I pull the base off the mill, turn it around for the second side, how close do I need to get it?

 

[Kernbigo]

They way you check doveltails is with 2 dowl pins ,and mike accross

 

[coffmajt]

It somewhat depends on how much precision you want in your slide. I would not want more than .001 in variation from front to back on a dovetail that will be used as a slide, and I don't think that should be a problem for a milling machine -- Jack

 

[Kernbigo]

That is true .001 max

 

[4GSR]

....snip...... So, if I pull the base off the mill, turn it around for the second side, how close do I need to get it?

You need it running "zero" from end to end when indicating it in, going off the previous machined surface. When you pick up the cut, leave your cutter about .0005"-.0010" off of the previous cut surface. Use a sheet of cigarette paper to touch off the milling tool with. Don't let it cut into the previous cut surface. Scraping will remove that last .0005-.0010" when fitting.

Ken

 

[Baithog]

That makes me feel better about breaking down the base and managing to get the second side reasonably parallel. I may still remove the glass scale so I can mill it in one setup.

As milled, before scraping, the x-axis table is .ooo4/ft and the saddle is .0005/ft.

The base, as shipped by the manufacturer, is .0004/ft guide side to gibbed side, end versus end. Pretty good, except the flat shinny potions n the middle where it is out .001. The y-axis saddle is is out .003/ft. No wonder the thing never worked right.

 

[tertiaryjim]

After scraping in my lathes cross slide, I found a tight spot. Didn't measure it but it took less than 1 tenth of a thousanths further scaping to clean it up.
The gibbs can only be tightened so much as there must be room for oil but if you have to gap them a few tenths extra because they aren't true, you have that much more
play and less rigidity.
Even with my amateur efforts, the lathe will now produce better finishes. Turning and parting operations are faster and smoother.
I started out scraping in the compound with a reground cutoff blade. The result was so dramatic and the work so difficult, with that blade, that I knew I must get some better tolls to continue.

 

[Bill C.]

That makes me feel better about breaking down the base and managing to get the second side reasonably parallel. I may still remove the glass scale so I can mill it in one setup.

As milled, before scraping, the x-axis table is .ooo4/ft and the saddle is .0005/ft.

The base, as shipped by the manufacturer, is .0004/ft guide side to gibbed side, end versus end. Pretty good, except the flat shinny potions n the middle where it is out .001. The y-axis saddle is is out .003/ft. No wonder the thing never worked right.

If it was my part I would call the manufacture about their poor inspection practices and see if the will replace this one for a good one. Just a thought.

 

[Baithog]

If it was my part I would call the manufacture about their poor inspection practices and see if the will replace this one for a good one. Just a thought.

I should have done that 7 years ago when I bought it. I knew I was getting a Chinese project machine, but this one turned out to be worse than normal. It will end up a little CNC mill when I'm done.

 

[Baithog]

After scraping in my lathes cross slide, I found a tight spot. Didn't measure it but it took less than 1 tenth of a thousanths further scaping to clean it up.
The gibbs can only be tightened so much as there must be room for oil but if you have to gap them a few tenths extra because they aren't true, you have that much more
play and less rigidity.
Even with my amateur efforts, the lathe will now produce better finishes. Turning and parting operations are faster and smoother.
I started out scraping in the compound with a reground cutoff blade. The result was so dramatic and the work so difficult, with that blade, that I knew I must get some better tolls to continue.

So what did you use for a straight edge to spot the dovetails? There's no way I can afford a camel back and I doubt anyone would loan me theirs