Can T-Slots be Repaired?
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  1. #1
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    Default Can T-Slots be Repaired?

    I recently finished reconditioning of a very old (100+) Steptoe horizontal mill that had been retrofitted with a Tree vertical head (fairly common in the 70's from what I've read). The Tree head is in perfect shape, has apparently had very light use; I know it had been literally sitting for the last 20+ years but the owner kept it lubed and in a conditioned space.

    The Steptoe mill was in surprisingly good shape for it's age. All screws, etc have only 10-15 thou backlash and look to be original. Some chip gouging on the main table bearing surfaces, but not that bad and lots of good surface after stoning everything down.

    Biggest issue is the table. In it's former life as a horizontal mill, had a couple of bad table crashes.
    A few light ones on the top of the table- but a couple of bad ones right at the T-slots, in a couple of areas.

    Small table (9" x 30"), and enough good slot to get the 6" Kurt bolted down in the center and towards each end, but off of center the T-slots have been all but destroyed and can't hold T-nuts.

    I'm pretty much resigned to being somewhat limited to vise-held work with this, but I was wondering about whether T-slots can be repaired via some method. Is it possible to get material welded or brazed in, and have T-slots be re-cut?

    I know I'm going to be told I'm nutz, but I've got this sickness with old American iron having restored a SB and Sheldon now living in my small shop and making me some coin on the side as well. I know I could send it off and have it planed or ground, but I've never seen a discussion here about repairing trashed T-slots.

    Are there machine rebuilders that do this, and if so, what procedure is used?

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    If you sent me this question as a rebuilder I would not give an answer without seeing at least a picture. Better in person of course. Theres many ways to repair t-slots, nothing compares to original as far as looks or strength, as I'm sure you know, if you could post a few photos you'll have much better luck retrieving a real answer. I will say, never have I repaired a t slot, using any method without paying some attention to the guideways, everything affects something in the machine tool game.

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    Show a pix and someone will help....I dont know how high, high up is with out a pix...Phil

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    You could weld and remachine using the right methods but it likely would distort and have to have other adjustments made after the process. You could also machine off the tops of the T and bolt on bar of the proper width. Then you have replaceable t-slots if an accident happens.

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    I suspect that making really strong brazed-in repairs will be difficult and likely will distort the table, due to requisite heating of the table for brazing prep, so that the ways and top will need to be rescraped. And it does take someone who really knows what they are doing to make good brazed repairs on cast iron. I think there are a few people out there who can do it well, but not many.

    However, a sub plate might be an alternative that would allow you to use the mill to near full functionality with minimal expense in terms or time and money.

    Rather than repair the table, if you really are suffering from love for old iron, you might make a pattern and get a foundry to cast it for you. Yes, it will cost a few bucks to get the casting done and then there will be the machining of the ways, and slots and scraping or grinding. BUT, you will not have to look at ugly repairs that themselves may not be full strength.

    Denis

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    Another way to do, if you are crazy, is to mimic the bolted-on hard ways that are common. Make up rectangles of steel or cast iron, mill the tops of the working surface of the table off, then bolt on replaceable 'ways' and regrind the whole thing.

    If you could bolt from underneath it would even be invisible. Or you could plug with brass or bronze over the tops of the fasteners, the way some places do.

    This would only be reasonable if you are crazy

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    Quote Originally Posted by BrianB View Post
    You could weld and remachine using the right methods but it likely would distort and have to have other adjustments made after the process. You could also machine off the tops of the T and bolt on bar of the proper width. Then you have replaceable t-slots if an accident happens.
    I think removing a lot of material from a casting that old might warp it as well. As others have said, pictures for real help.
    I will say there are many specialty alloys for welding to cast and that pre-heat is critical to both quality and strength of the job so finding someone with an oven big enough would be a challenge it you weren't doing such a small item. N99 and similar rods are pretty typical but I've found Inconel to "wet into" the cast really nicely and it has a closer CTE to cast than much of what's out there. Of course it's $200/lb for the filler and, er, not the easiest to machine afterward. I will say I have yet to experience a failure with this material and that includes some pretty big patches in heavy load-bearing wheels.

    By the time you prep the part, pre-heat it, weld it, cool it back down slowly, machine the repair area, and address the warpage from typical welding, I start to wonder how hard it is to just make a new table, if it's the size I think it is, those are pretty tiny.

    Oh, hey, I remember now... spray-welding! Still a guess with no pics, and I have no personal experience with the technique ( I'm thinking HVOF here) but it was billed a great technique for building up worn shafts and other critical already machined parts with the absolute minimum of distortion.

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    Not sure i would weld anything on it. I spray welded som drill holes on a table 40 by 20. Warped the crap out of it , could have been the sub plate that never got removed with the rust between it. But it-needed turcite so i machined it strait on a planer. Then did the turcite on the bottom. Probably not the right way but it turned out really good. Then the hole in the middle, after getting the table back on and adjusted i milled a piece of dura bar with the t slot in it and milled the hole and bolted it in. It was a cnc so getting a tap fit in the table was easy. So far so good got a year on it.


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    All those other spots were the spray weld slightly harder too


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    Quote Originally Posted by tobnpr View Post
    Are there machine rebuilders that do this, and if so, what procedure is used?
    Least work is to adopt another mill that is already in good condition. Not a joke. "New" labour, burdened is bought at today's rates.

    "Old" Iron, abandoned and orphaned is "out there" as to horizontal mills with no love - but decent tables - going far more cheaply.

    Second-best is to adapt an entire table that is already in good condition.
    Same- again as to sourcing. Part-outs off those weary mills as have not escaped to a smelter just yet.

    Adapting doesn't REALLY have to even be the same family, clan, or tribe of mill as donor, "close" can work. You'd have mounts & dovetails to "frankenmerge". Not "trivial" but lower risk of bad news than tying to repair a lot of linear inches of Tee-slot edges and creating a pretzel.

    EX:

    I've got a really, really old "universal" (swiveling) table complete save for the knee and "Z" axis setting in the shop as I type.

    Came off a B&S #1 universal mill of somewhere around War One vintage.

    Dunno how it was tooled and used, 'coz from the wear on the long-axis screw it surely WAS used, but the table & Tee-slots are virtually undamaged. hardly a mark, anywhere. Most likely spent its working years with a sub-plate and fixtures atop the table most of the time.

    Third best is to mill a new table from the solid. Which is not sane. I just happen to have some 8" X 3" X 30" former G&L hor-bore bedway that might do!

    Even so "not sane". Plenty of old mills in better table condition than your one.

    Best could be to bolt-on watcha actually NEED, not wish-for, and JF use it. At least the fees and freight are cheap!


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    A "grid of holes" plate fixed on top of the existing table can work very well.

    I did such to a little BCA jig borer / mill. I found that machine very restricting as it has built in rotary table with radial slots on rather than the longitudinal slots of a conventional table. I used one of the aluminium optical breadboards from Thor Labs with 6 mm holes in 1" square 5 spot dice patterns. Too light for your machine but maybe gives you some ideas. Worst point with grid of holes is cleaning out swarf. I put short lengths of all thread studding in the ones I couldn't just blow through. Less than ideal as the studding had to be pulled to use a hole but not, in practice too much of a pain. Possibly aligning your holes with the pre-existing slots would make blow through cleaning followed by rodding out the space practical.

    Another approach I've found effective for things that cannot be safely welded due to warp risks is to glue and screw replacement sections on. Modern metal bonding adhesives from the like of Loctite et al are very strong and have very thin glue lines so alignment can be held. Screws are more to prevent peel loads than truly structural so the don't have to be that big. I'd mill the tops of the Tee slots right off, fit appropriate size bars, making sure the screws are a little below the surface, fill the heads with a metal loaded filler and mill the thing flat. Done carefully it will be sufficiently accurate.

    As Thermite says the effort is, objectively, no way worth it. Always better to start with a good one than to spend time on a fixer-upper.

    Clive

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    i fixed one that had the underside of the slots chewed by using either too small t bolts or even hex head bolts with a bit of weld on them ,as Ive seen done.........anyway ,heat is out IMHO ,so I just ran a dovetail cutter along the slots ,and evened up the undersides ...then made a set of t bolts with sloping engaging surfaces.,and also some long T nuts for a vice ,one long T nut per side for 2 hold bolts per side......Cincinnatti planers used a replaceable angle insert in the T slot.

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    This machine is an example of replacing the t-slot top. The mill is the same vintage as yours. Cast iron is very soft. I have no idea when the repair was made.

    Davis & Egan Machine Tool Co. Millier Page 2

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    Now that is a lotta drilling, tapping, and machining. Good job, though, if ya don't mind a lotta scraping too.

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    Quote Originally Posted by neilho View Post
    Now that is a lotta drilling, tapping, and machining. Good job, though, if ya don't mind a lotta scraping too.
    Pre-drilled and tapped "grid' plates were mentioned. I have two that were also "optical bench" goods. Pretty cheap as suplus. WHEN they show-up.

    Drill & tap a similar feature into the damaged OEM table? One can.
    Yah don't usually NEED a full end-to-end grid with 100% coverage, after all. A handful of well-planned ones and a bit of flexible kit to utilize them can go a long way toward covering more needs than not.

    Another "convenience" approach is to lay-on sub-plates made of the modular Tee-slot shiney-wood extrusions meant for tabletop CNC router-critter builds, "OEM".

    Not as strong as the original CI, but very often they do not HAVE to be, either.

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    Wow! This site has changed a lot since I last visited. This is a good think IMO. I'm, sure it's a bad thing to many as well. For sure there was a time when a question like this one would get way more posts telling the op to post on the hobby forums and leave this site to pros only. I don't mean to rattle any cages or start trouble because I really feel this site has become more tolerant of the non pro group. At the same time I have the utmost respect (and envy) for all of you Profesional people.

    I have the same issue with table of a very old Index vertical mill I cleaned up and repainted a couple of years ago.
    Here is a link to the photo of my table :
    "Repair" a damaged mill table with a pallet???

    I put the mill back together with a vfd on the spindle motor. The table feed motor needs its own vfd which I can't justify buying. I used the mill one time since the prittying up I did. I have a piece of 1" aluminum plate that I planned on drilling, tapping and putting insert in but didn't bother.
    The reason I got this mill was bacause I already had a fair amount of tooling I got with my old Burke horizontal mill. I should sell them both.

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