How do you repair the T-Slots on a milling table?

[Nelson]

Hi Guys,

Milling table has damage to the T-Slots (pieces missing).

How do you effectuate repairs properly?

Thanks,


Nelson

 

[Tony Wells]

Need pictures. Too many variables to recommend a specific procedure.

 

[Nelson]

Something like this only worse, where the actual T-slots are ripped off and jagged.

 

[Tony Wells]

I have seen, in extreme cases where people would mill out a pocket of an appropriate size and shape, and fit in a machined insert made of cast iron that was drilled and counterbored to mount, then drill and ream for press fit dowels. The CI piece would of course need to replicate the section of the table being replaced. A small amount of stock would be left on the surface for a light skim cut, and a lapping in to match the rest of the table.

Under no circumstances should an attempt to weld be made, unless exotic processes are involved followed by a complete remachine of the table, including the way surfaces and /or dovetails.

Of course, one thought might be to find a replacement table from a similar machine, or simply find a suitable table and mount it directly on top of the ruined one. Of course, this would sacrifice a bit of Z axis travel.

 

[Nelson]

On the small dings, can I make a metal-filled putty by combining cast iron shavings and devcon or some other epoxy?


Thanks,


Nelson

 

[Tony Wells]

You certainly could. I have some Devcon two part putty that becomes a machinable solid once it sets. It contains steel/iron powder. I'm not sure you'd get a color match. In fact, the stuff I have wouldn't match someone's nice new table lapping job. It's a dark iron gray. I can't think offhand a functional reason for doing it on a table no worse that your picture, other than perhaps filling with swarf and chips and making dragging a vise or something across it. But it's a bad idea to drag something across a dirty table anyway.

In the case of the more extreme damage you referred to, I can't think the Devcon or any epoxy type material would be a suitable repair. Only if it were in an area that would never be used, but you wanted it to look a little better.

Truthfully, in many cases, there is too much focus on appearance of machine tables. Those accidents really have little effect on function. If there is a hole through the table, that's one thing that should be repaired, but otherwise, just make sure it is flat overall. Dead file it, stone it, lap it....and use it. And disclaim all of it to your friends .

 

[Tony Wells]

Heh....good point, Jack. That's one reason I try very hard to find a way to work in a vice or indexer rather than straight on the table. And then, I like to put a sub plate on to protect the table. But then, I'm all manual, so I don't really have any excuses like the button pushers who blame the programmers, who blame the operators who qualify the tools in Z.

 

[drawfiler]

I have done this several times over the years, the first machine was milling table which I did 30 years ago and still looks like new. This what you do
1 remove the bearing plates from each end of the table and make some stand offs to fit into the screw holes, in this way the table can be fed further so the tees can pass under the head.
2 get some mild steel flats longe wider and thicker than the topos of the tees
3 get a length of drill rod say 5/8" dia
4 mill the tops of the tees away leaving thew vertical part in place
5 using the mill as a driller drill the plates and the vertical part with a sutiable coarse tapping drill
6 counterbore with a 5/8" drill into the plate
7 open the plate out to clearance size of the thread
8 tap the vertical web
9 machine a thread oto the drill rod and an undercut just back from the plain part
10 coat thread in locktite
11 screw home with grips and it will shear on the undercut
12 repeat for all the other holes at about 6" centres along each strip
13 mill the edges of the plates to size
14 trim off all the broken bits of the studs
15 get table top ground and use.
Peter

 

[pjf134]

Use microweldersmicrowelding.com, It's a low heat welding process to fix dings in mills and lathes. I don't know how much the little machine costs, but I would expect it being less than a regrind.
Paul

 

[drawfiler]

The problem with cleaning up the top surface only is that the underside of the tee is where the bolt bites and if the surface is chipped you will have trouble in locating your work exactly. to do the job I ave described above on a36" table takes only 1 day, so do the job properly!
Peter