Tram & Nod on a Seig 2.7 (LMS 5550 HiTorque)

Thanks all.
I bought some steel shim stock, goes down to 0.0005
I'll look into Onion Skin paper. I think I'm going to go ahead and try my plastic shim stock while I wait for the steel to arrive.

Any thoughts or comments on how to get shims under the column? I'm assuming that once I loosen the 4 bolts I'll be able to rock it a bit and slide shims in. However the two alignment pins give me a little pause.

I'm I going to have to use some sort of hoist or jack to lift it up a bit?

-Dave
 
You could try putting some blocking under the head and lowering it down on the blocks, sort of like a jack in reverse. If you need more lift power, engage the Z axis fine feed.

I used that approach when I replaced the belleville washer on the back of my column with a 1/2" thick steel plate.
 
Use a small jack and a block of wood (to protect the quill nose) to raise the front. Pull the head forward to get to the rear part of the base. Just loosen the bolts enough to get your shims in.
 
As is often the case, there are a number of ways to address your problem. Choose your favorite! :). Part of the reason this hobby is fun, everyone has the opportunity to do something different and creative. Sure keeps me coming back.

I'm not sure your head+column weighs enough to endanger the quill nose but, hey, it's cheap insurance. I like over-doing it if it's not difficult to do or un-do!
 
if the column base is like the 3690 there is space to wedge up the column and slide in or out the shims once the bolts are loose,, shims are best if cut in U shape spanning to bolt,, leave extended tabs to aid in installation and removal,, these can be cut away once the correct shims and placement has been found..
 
Back to this task, fortunately (I guess) other distractions in my life prevented me from diving in and screwing things up.

I now have a set of steel shim stock, down to 0.0005
I've also finally made as accurate measurements using a bar a made to reach the corners of the table.
I'm embarrassed to say that I had gotten totally tripped up by cosine error, although I'm sure a lot of you have been there.

Turns out that my X table is setup pretty square - tram & nod. Here are the 4 corner measurements (looking down, from the front):

-.0015 ............ .0015
-.003 ............. .000

That doesn't look that bad to me, particularly in X, that's .003 over 27"
Y is much worse being .0015 over 4.5"
Not sure if I still want to try to reduce the tram, but the nod is bad enough that it's probably worth a try.

I took many, many measurements at different distances from center (how I finally realize I had cosine error).
Multiple measurements again (doing it correctly) confirm the above numbers.

More interestingly to me (and my question) is that I measured 0.002 crown on both sides in the X direction
AND .003 crown on the left end, .002 crown on the right end (in the Y axis).

The question is should I stone the tabletop to remove the crown in Y? clamping is going to distort the thiner brass and aluminum work I intend to mill. I might be able to also reduce the crown in X by working the center a little more, but I'm less concerned about it.

Also, I assume that the "Correct" way to deal with this would be to remove the X table and set it up on a surface plate. However the amount I'm dealing with here probably doesn't' warrant that. I'd guess that disassembly and reassembling could change the table by small amounts considering that this is a cheaper small asian mill.

The crown in Y is noticeable enough that parallels and setup blocks and squares will rock front to back.

I should also add that the many measurements I took and examination with straight edge and shims all confirm that the crown is real consistent / smooth (a hill not lumpy).

-Dave
 
Depending on the size of the thinner brass/aluminum pieces you want to machine, you may want to consider making a tooling plate. Bolt it firmly to the table and machine its top surface flat. There are lots of designs out there (I based my plate on the free Fignoggle drawing). You also don't have to drill/tap the entire array of holes, just the ones you need at the time.

Harold Hall has a number of low-profile work holders that can be easily adapted to a tooling plate. I made some longer ones so I could machine a "tee" profile in an aluminum bar so it would fit the slotted guides on my table saw (the manufacturer made the dimensions nonstandard, probably so they could capture more $ from their customers). I also made a sine table that mounts on the plate so I can fabricate tapered pieces.

When I made mine, I drilled and reamed a center hole for a dowel pin so I could indicate it in for "0,0". With that as a reference I can precisely place additional holes as needed.
 
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