New Mini Mill Bed- What Material?

[llhots]

Hi everyone,

I have a Sherline CNC Mill that I have converted to a larger, more rigid setup from A2Z tools. I have had tremendous trouble tramming the mill. I finally discovered that the mill bed itself is warped.

Unfortunately, the bed is warped by a significant amount-- about 16 thousands in the across the short side (Y-axis or depth). I have contacted A2Z, which had a good reputation but was bought this summer and now has closed, or else is in the process of going out of business.

I checked it many different ways- surface plate, Traminator etc. I know the bed is bad.

In any case, the Z column is fine and the Y axis base is as well. All is made from anodized aluminum. What I am wondering is:

1. Can I add another piece of aluminum to the bed and flycut it to true it up? This might work to make at least a temporary level bed.

2. I am in the process of taking measurements off the current bed to have a new one machined. My question is, what steel is a typical machine bed made of?

Thanks in advance. I've learned so much from all of you here.


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[kvt]

So A2Z is going out of business. I was thinking of getting some stuff that I had seen last year but had to wait on. Their site still looks good but alot of the pics now say not photo avaible.

 

[T Bredehoft]

I would only consider cast iron for a mill table. I don't know enough to specify the grade, but some grades are better than others.

 

[derf]

For a mill of that size I would use 1" aluminum tooling plate and bolt it to the bed.. Tooling plate is ground flat, so I would just shim in the affected areas.

 

[hman]

1. Can I add another piece of aluminum to the bed and flycut it to true it up? This might work to make at least a temporary level bed.

OK, dumb question ... couldn't you just flycut the bed itself?

 

[llhots]

Thanks for the tooling plate suggestion. I guess I'll try that first. I thought of flycutting the bed itself. It would ruin the anodized finish, but then I'd much rather have a square bed.
Very disappointing to see A2Z fall from a legitimate quality supplier to someone who doesn't return any customers calls, nor their suppliers and can produce pieces with this much warp.

I will also continue to explore the possibility of having a new bed milled so I'm not reliant on a tooling plate. Thanks again.


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[Tony Wells]

I'd contact Sherline directly or find another distributor if I wanted to retain originality. Otherwise, since this is a smaller machine, tooling plate would be a good solution. To remake the entire table seems impractical. This assumes that the running surfaces are actually true themselves.

You would also need access to a larger mill that is in good shape, and/or be prepared to do some scraping. If you were to choose CI, ASTM A48 in one of the classes best for machine tool parts. Preferably something cast in the Meehanite process. I personally see no need for CI on a Sherline.

 

[llhots]

Thanks everyone for the suggestions. I am going to try and use a one inch MIC6 tooling plate that I bolt and then flycut and then will mill in the necessary slots with a woodruff cutter. Hopefully that will give me a decent surface to work from...


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[Tony Wells]

Cut your tee slots before you finish the top. It should be pretty much the last thing to do.

 

[Andre]

OK, dumb question ... couldn't you just flycut the bed itself?

Mill tables, because of their weight and dovetail oil clearance, tend to sag to the side extended further from the saddle. If you were resurfacing something such as a motorcycle block, it would be usable but still slightly convex. If you were flycutting an inline four on a typical old Bridgeport, it could be too concave to meet specs.

The table can be flycut, but take a lot of measurements and more importantly make sense of them. Vary your depth of cut to keep the table as flat as possible trying to avoid the table becoming convex. The lighter the mill table the less it sags, but it will always sag slightly. You'll want to cut deeper in the center than the ends, maybe by only a few thousandths.

For example, adjust your X axis gibs properly then take a skim cut till your table cleans up, use your straightedge and lightly weigh it down in the center. Use feeler gauges to measure the gap at the ends of the table, average those two readings and that's how high the center is. Then take another, ever so slightly deeper cut in the center 1/2 of the table, then another very light cut on the center 1/4 of the table a thou deeper than your previous 1/2 table pass. Measure as you go and plan out how much you have to take off which parts of the table to keep it flat. Then once you get close, you can scrape the top since you have a surface plate. To keep things simple, you can use red oil paint as a transfer dye. Make sure to scrape "Straight down"