adding a back plate to my mini-mill, but some problems appeared

[Anko]

Hi to all

right now i´m putting a back plate to my mini mill column, i made from a scrap steel plate, all going very well, i made the holes to the base and column and put the screws everything in place, so were are the troubles?

well, once the plate was instaled I proceed to tram the mill for real, following the nex steps:

first i will tram the colum true to the table, then i will lose the four screws of the head and tram the spindle head true to the column travel, done all, the mill should be ready.. and then finally i will be able to get real square corners and perfect finish with the fly cutter....

but soon I realize that in the first step, i should not put the column straight to the table but has to be straight to the table X and Y travels, well, i took some readings with the dial indicator, the results are:

in 23 cm of the table I have 0.06 mm of runout, that means that the suface of the mill table is not parallel to the bottom, and in the Y axis has a runout too....so i´m imagining some like this:

i´m getting a good head pain trying solve this little problem, any thought on this?

i will apreciate very much your opinion on this

thanks


Saludos

 

[rudydubya]

Hello Anko. With only 0.06 mm of runout sounds like you're getting close. Nice job on the back plate, by the way. Just guessing here also, but have you checked your X and Y gib adjustment? I can imagine a situation where the gib screws are tightened more at one end or side of the table than the other, maybe allowing a little play in the table as it reaches the tighter/looser end. Does your measurement change any when you lock and unlock the X or Y lock handles?

 

[Kermit]

You need to shim the bottom half of the spindle head/housing for adjustment of the Y axis. I believe there a couple of threads on that here already. One with a very good set of pictures on a mill very much like the one you have.

Kermit

 

[TroyO]

I found my ways were very much out of wack on mine, and that the TOP of the table was also very bowed. (.006"... or .15MM) shim would fit in the middle when it was on a flat surface.

Find a flat reference surface (I used a granite countertop piece) and start measuring to figure out exactly what is wrong... is it the bottom ways or the table surface?

If the ways are straight(ish) and it's the top that is out, I flattened mine by using the granite slab I had and spray glued sheets of wer/dry sandpaper to it.

Then you "Lap" the table, start by covering the table top all over with magic marker (Or Dykem if you have it) and start rubbing the table surface on the sandpaper. I used a figure 8 pattern, and tried to keep about the same number of 8's in both left and right hand. Eventually the bright areas will grow, and the dyed/marked areas will shrink. Keep re-applying the dye and lapping (and replacing the paper) until the dye starts to rub off evenly all the way across. It should be pretty darn flat by that point. It sounds like yours may be "lopsided" so you might want to lean extra hard on that side. This took me a couple of hours.

I have about .0008" over the whole table ... which is about .02 MM.... which is plenty fine for what I do.

(PS... not sure about my metric conversions, feel free to doube check/correct me!)

 

[Anko]

thanks for the responses

JorgensenSteam:

in the first place i was thinking in that, but i realize that the column should be straight to the travels, not to the surface of the table, reasons? i try to ilustrate what happens if the column was straight to the table surface:

still, of the column is straight to the travels and the surface is out of parallel with the axis direction, results will be the same

in that case, everytime that i clam a workpiece i should shim it to get straight to the axis direction....that is because i want to solve this problem
thankyou anyway!


rudydubya:

yeah, when i tight the loking screws of the gibs i got some 0.01-0.03 mm of variation, ??? but is strange
because if i tight a little more the gib set screws the axis get strongly hard to move..

i will get a better look en the gibs


Kermit:

yeah i have looked thats post more than one time, i got the inspiration from there, but they talk of the column flex and tram, nothing about a table runout...
still very good post, my back plate is based on that!

TroyO:

cheking the table on a surface table is an exelent idea!, but i do not own one of that yet... :-\

but you give me the solution: i will carefully sand the table like you did and see if i can improve the acuracy.


but before that i will check the gibs, when i try to move te table to see if there are a runout the thing seems to be very firm, but when i apply force in the Z direction, with the dial indicator i can see some movement, i will check this out again

thanks you guys, i will post my improvements

Saludos!

 

[TroyO]

Try going to a place that does granite countertops and ask for a cutoff or sink cutout. Another place to look is a home recycling place... they sometimes have countertop sections.

Lastly, you could look for a tile store and get a 12 or 18 inch tile (300 MM - 460 MM?) granite tile.

While none of those are "real" surface plates, they work OK in my book... for now anyway, LOL.