A crack in the saddle of my hobbymat md65 lathe and the possibility to restore this

[Rosita]

Hi,
I am a novice (mini) lathe user and live in the south of The Netherlands near Eindhoven. I own a Hobbymat MD 65 which hasn't been used for over twenty years. Apart from some flash rust everything still runs smoothly.

Now I have an problem with the saddle of my lathe. This plate where you mount the toolholder has a tiny crack and starts at the beginning of the saddle through the two threaded holes, which hold te toolholder, and a little further (11 mm from the second hole)
I took some photo's and and want to ask weather or not this can be restored. Repaired maybe.
The first two photo's are an overview of the whole assembly (just to avoid mistakes in the names of the parts)
As the other photo's will show the crack extends to 11 mm over the second thread hole. Total crack is therefore some 35 mm. It appears that the crack on the top is 11 mm longer than the bottom side one.
I don't know how the crack came to life. Maybe too much pressure then fastening the tools in het toolholder. I don't think the crack started with adjusting the gib.
(the gib is alright btw).

Of course there is the possibility of doing nothing and let the saddle as it is. But then I don't know what happens when tightening the tools in the toolholder. And I don't know what will happen if I start machining rods for instance. Because this will give some pressure too.

Second, I can drill a small (3mm) hole at the end of the crack (top side)

I also don't know what material is used for the saddle. Just plain steel, cast iron or cast steel. The thickness of the saddle at the crack position is about 8 mm. The bed itself of the lathe is flattened cast iron I think.

Anyway my original plan was to widen the crack from top to bottom and then weld it. Mig/mag. But that seems pretty drastic, especially the flattening on top and the bottom and 'repair' the threaded holes.
I could also have a sheet of metal say 3 mm and attach this firmly with screws on the top of the saddle. But then I have to consider what happens with the tools to bring them in line with the center.
Maybe metal glue could do the trick (after drilling the hole at the end of the crack). But to get the glue into the crack I think I have to widen mechanically the crack for a moment. Don't exactly know how to do that and also I don't know what glue to use. Loctite?

Some people with broken (cast iron) stuff suggest brazing. I don't know (yet) how to do that. What kind of brazing and how to start and with what.

So it is obvious that I really need some advice about this problem.
Is there someone who could help me on this or think a little on the do's and don'ts.

I will use this lathe only for hobby purposes. Don't want (yet) to make difficult workpieces. I don't need a thousands of mm of accuracy so to say.

Ok, any help will be very much appreciated.
Peter/Rosita

 

[Steve-F]

Hello Peter, First, nice pics:<) The first thing that flashed through my mind was to put the cross slide in a mill or good drill press and drill a hole and tap it for the largest bolt or cap screw that it can accommodate, just above the gib screws, in the center of the mass that is the thickest, and draw it back together with it. It's a casting, so welding is sort of out and the bolting of it ,in my opinion, should get you back in the game.

Edited to say maybe 2 bolts set apart, 1 in front and 1 between the 2 holes.

 

[RJSakowski]

Welcome to the forum Peter/Rosita. First of all the saddle thar you are referring to is called the compound, at least over here.

As to gluing, no. there is no glue strong enough to hold. Your compound is most likely cast iron based on the crack. Steel 2woulden't crack like that. Cast is difficult to weld, even more so if you want to keep the precision geometry. Brazing is a possibility but I would take it to a professional. Even then, there is a possibility of warping. If brazed, the threaded holes would have to be retapped. Your best solution may be to make a new compound. It is fairly simple geometry. Doing so would require a mill though. A possible solution would be to bore cross holes and use tie bolts to hold the split together. To stop the crack from extending further, a small hole is drilled at the end of the crack Otherwise it will continue to grow like a crack in glass.

 

[Steve-F]

Oops, yes, it's compound:<)

 

[George R]

I would weld it grind/machine it flat and re-tap the holes. It is cast, but cast is not difficult to weld if you use the proper wire, preheat, and post heat. Crown Alloys make a nickel-iron-manganese MiG wire the works well and will result in a much better repair than brazing.

The other option in to use it, watch how the crack progresses, and make a new one when needed.


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[Al 1]

I personally would clamp both ends. Grind V's in cracks, Pre heat and TRY (T I G) brazing with silicon bronze rod. When finished Cool slowly and then File the surface flat. Al.

 

[Litshoot]

I think al has best option. Drill the end of the crack, v groove the crack, Pre heat in oven for too long. Take it out tig braze isnmy choice, but torch brazing does offer less warping as it keeps heat spread out. Make sure part stays hot entire time,at need to go back in oven to soak back to even set temperature. Them when finished cool it down slowly in same oven dropping temp a few degrees ever few minutes. You want to take hours to cool. Measure it and see if any warp ha shown up. If it's good mill it flat tap the holes. You'll have an nice silicon bronze stripe on the part to show your work when finished. If you pay someone to do it they will most likely rush it as it's a job. Practice some and give it a go.

 

[Richard King 2]

I like RJ's fix. Or you can check and see if you can buy a new one.

Another idea would be to install a steel plate on top and bottom using flat head screws. Welding will warp the part even if it is preheated. I am a professional machine rebuilder and making or buying one seems easiest to me. If you make one, buy some grey iron Class 2, 3, I have a good friend, Jan Sverre Haugjord in Oslo who is a good machine rebuilder. He could do it for you. He was a hobbyist and has been rebuilding machines as a hobbyist for 10 years now. I have his email if you want it. Message me. I cut and pasted the machine name in Google and there was a few places that sell parts for them.. He has several You Tube shows too. He knows people from all over Scandinavia who are hobby rebuilders too. He travels for work too....you never know, he may traveling your way sooner then later.

 

[Rosita]

First of all: thank you very much for the different but valued possibilities.
So the part is called a 'compound'. In the parts list I have (over here) it is called a 'saddle'. That's why I took a picture of the whole assembly and listed the names of the parts. (so much for complimenting myself...)

The brazing and welding solutions seems hard for me to do. I did take a one year (beginners) course in welding and learned the basics of stick- mig/mag- en tig welding. I don't own a tig welding machine. Heating up the part in the oven also seems a good preparation but I don't have one and none of my (few) friends either The brazing which leaves a nice silicon bronze stripe appeals to me however. Kind of thing you would be proud to show others. But as I said for me at this moment and with my lack of experience it will be too hard.

Making a new one falls in the same category for now. But I will keep in mind the the suggestion of Richard King 2 to get some grey iron class 2 or 3. And maybe through him try to contact his friend in Oslo.
Buying a new part is not possible but found a second hand part on ebay. But this one is for newer models which have 5 adjusting screws instead of 7 as mine has. On top of that the gib has a slightly other form which why it is impossible to replace the compound.

Leaves the suggestion to 1) drill a hole at the end of the crack and 2) drill a hole on the thick part of the compound, just above the gib; drill it through the entire width of the compound, so also through the crack, and get a bolt in and use a nut to 'tighten' the crack.
This I think I am able to do.
The thickness of the part just above the gib is 8.4 mm. If I use a 4mm drill this leaves 2.2 mm 'flesh' on the side. And if I start say 7 mm from the beginning of the crack I think there is enough metal left for tightening.
The outer diameter of the bolt and nut is less than 8 mm, so if I can keep the hole in the middle of the thick part I don't have trouble of sticking out nut or bolt head, So don't need to rework them.
Maybe it is wise to drill a second hole just between the two threaded holes parallel to the first hole for the bolt and nut. This way if I mount the tool holder and have two tools in, the pressure on these spots is more or less equally spreaded on both sides of the crack. And the crack is held together in tho places.

As said, the 1) drill a hole at the end of the crack won't be a problem.
The number 2) drill a hole for tightening the crack is a little more difficult. I wil have to practice this. I have an ordinary table drill and have some 8 mm steel which I will cut to te same dimensions as the compound.
The I will do some exercices.

When I succeed of course I will let you know. I think with this solution I can carry on a little more until I find a way to make a better (nicer) solution. But by that time I know I didn't do much harm to the compound.
Again many thanks for all of you who were willing to participate in getting the problem solved. I really much appreciate this.
Got me thinking and got me wiser.

Peter/Rosita

 

[Litshoot]

Brazing can be done with a oxy acetyl torch similar to the way solder or tinning is done, but again as someone who hasnt brazed either i have no idea how complicated it really is
As for drilling the hole, its somewhat frowned upon but i would recommend turn compound(saddle) and space it up. although again not popular used the lathe with a drill in a colette or chuck, to drill through the compound, it will keep it aligned and move straight in. while you drill through. recommend nut and bolt over tapping the compound.