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Ajax AJ8 horizontal Mill - cracked casting

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Mark Davison 121/03/2018 07:58:08
58 forum posts
14 photos
I've just bought an old Ajax AJ8 mill that has a crack in the main housing (an open bottomed box approx 12" square and 24" tall). The crack runs from a large aperture in the side that accepts the switch gear diagonally out and down to the bottom corner by one of the 4 feet, approx 6" long (a such it has cracked right through from end to end). The wall thickness is unlikely to be much more that 1/8" but I've not measured it (could be 3/16"). I'll try and put a picture up this evening.

Any recommendations on how to fix it? The options as i see it;
Braze - id have to pay someone else to do this.
Weld without preheat - I could try this myself but am reluctant.
Epoxy steel stick.
Patch and bolt across the inside using epoxy to give me a flat surface press the plate against. There is a thick flange at either end of the crack that I could drill and tap to add some thick straps.

Edited By Mark Davison 1 on 21/03/2018 08:00:01

Brian H21/03/2018 08:05:33
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1294 forum posts
99 photos

How about having it stitched?

Brian

Mark Davison 121/03/2018 08:07:26
58 forum posts
14 photos

Is the wall thickness sufficient? Is that an option if is cracked end to end?

Mark Davison 121/03/2018 08:12:46
58 forum posts
14 photos

aj8 cracked casting.jpgaj8 cracked casting 2.jpg

Mick Henshall21/03/2018 09:04:19
523 forum posts
29 photos

Hi Mark,

I would have thought stitching (as they do on engines) would be worth a try, or could you patch with a plate extending each side of crack and bolting through and nutted

Mick

Muzzer21/03/2018 09:33:16
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2904 forum posts
448 photos

I doubt if the wall thickness is as little as 1/8" somehow.

But what makes you think there is any need to "fix" it? It's probably fine as it is unless you find the cosmetics offputting. Consider this the other way - is the casting likely to flex or possibly even fracture due to the work you will use it for? Again, it seems unlikely. Or imagine if you tried to break it up - would you succeed? What do you imagine would happen if you didn't fix it? Furthermore, it's securely bolted to the rigid base although it obviously wasn't when somebody managed to drop it.

I'd suggest you clean it up, fill the crack with epoxy / paint it - and get on with using it.

Murray

Journeyman21/03/2018 10:21:25
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627 forum posts
98 photos

If it were mine I think I would go for a cold cure! Any heat from brazing or welding is likely to induce stress. It will be interesting to see if anything moves when you unbolt the column hopefully there will be no lateral movement in the crack. If you are worried about this a repair could be made while still bolted to the base but slightly more difficult to get to the inside.

I think a steel plate on the inside would be the best option. Make the plate as large as possible from the base up to the opening and as wide as possible ground to fit into the corners. Clean up the inside with an angle grinder, sander etc. to get back to bare metal. The inside surface is unlikely to be flat so use plenty of gap filling epoxy and clamp the repair plate in place. Don't overdo the clamping it will add stress just enough to hold the plate in place while the epoxy sets. Once set add a few small C/S bolts with nuts on the inside, grind / sand the heads to blend in and then fill and paint.

John

Clive Foster21/03/2018 12:35:52
1896 forum posts
62 photos

Murray has the right of it. Nothing is going anywhere so opening it up a bit and filling with an epoxy something, I've used metal loaded filler (Devcon et al) with success, is the sensible way to go.

Plating as suggested by Journeyman can be very effective but you need to be vey careful with steel plates. Especially relatively thick ones. I have seen more damage than the original produced by such repairs where the thick, poorly seated backing plate broke the casting when the screws and bolts were pulled up tight. Relatively thin alloy and a metal loaded gap filler is safer. The alloy will bend and metal loaded filler is surprisingly strong. Approaching Mazak and similar castings. Steel, I think, is best reserved for when you can clearly see and work from both sides. Its the epoxy which does the load transfer work, not the screws holding the plate, so nothing needs to be uber tight. But it can be awfully difficult to feel whats going on and inadvertently over-stress things. Especially with thin castings. How do I know?

When no other option would do I have welded castings back together without preheat using ordinary, albeit ductile, stick welder rods. The technique is really of the "field expedient" class but is well known to work well if done carefully. Basically the crack has to be opened up and thin layers of well put on both sides using a small rod and low current. When adequately built up final close is done with several passes of a larger rod. Things must be left to cool fully between passes and the weld metal needs to be peened with the chipping hammer as it cools. Peening largely counteracts contraction during cooling minimising extra stresses in the casting. The initial thin layers control carbon migration and similar effects around the joint line which otherwise would be very brittle.

Slow old job tho'. Be futzing about for a day or more with your crack so completely inappropriate here.

Clive.

Neil Wyatt21/03/2018 13:22:44
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Moderator
16757 forum posts
689 photos
76 articles

I would screw a plate on, but give it a rough surface texture and rather then making it really tight I would fill the gap with JB weld. Make the screws slightly overlength and use a dremel to flat them back flush.

Clean the surfaces really well first.

Neil

richardandtracy21/03/2018 14:35:23
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938 forum posts
10 photos

I agree with much of what's been said about not welding.

I don't think it would have been caused by dropping the casting - the bottom flange would also have fractured. It may have been there forever - a contraction crack from when the casting was made & originally puttied over because the area's unloaded and is now showing up decades later. However, I think there is a chance it may have been caused by working loads. If it had a high power, fast, power feed, the column would be twisting as the table went from left to right & vice versa and then braked. The crack is as the max shear stress angle and the column attachment bolts are on the wrong side of it, which is pretty much what you'd expect from an over-stressed item loaded that way.

Solution, in my view, is to avoid heat totally. If there is a fast & powerful power feed, do not use it. For the crack, cold cure epoxy in the crack & consider the idea of a properly bedded down repair plate. If the power feed caused the problem & is now gone/not used, there is probably no need to put in the repair plate. However, keep an eye on the crack & see if it re-opens when you're using the machine. If it does, correlate it to the type of action that's opening it up and consider if it's frequent enough to warrant doing something about.

Regards,

Richard.

Mark Davison 121/03/2018 15:15:38
58 forum posts
14 photos

thanks for all the suggestions. i will give the epoxy and plate a go. i may try it without bolting first and see how it fairs. as for power feed, i don't believe it had one, although i do plan to fit a stepper motor to the x axis.

Gordon A21/03/2018 15:39:13
142 forum posts
4 photos

What about a plate on the outside? It could go the full width of the column and up to the height of the opening. With the edges filled and smoothed and the whole thing painted it would look like it was always part of the original casting would it not?

Gordon.

Gordon W21/03/2018 16:05:46
2011 forum posts

From the photo it looks as if the crack is not full length. If so, drill a hole at the end of the crack to stop it spreading. I would go with epoxy and plate.

Clive Brown 121/03/2018 16:42:23
287 forum posts
7 photos

I'd also consider reinforcing the column by fastening a sturdy steel plate firmly over the switchgear opening where there seems to be a reasonable machined flat surface. Well fitting bolts or dowels perhaps will take any shear load. This will provide strength at the upper end of the crack

Mark Davison 121/03/2018 16:44:42
58 forum posts
14 photos

i have some 3mm steel plate ear marked or that already as i think the original is missing

geoff adams21/03/2018 17:26:21
130 forum posts
144 photos

hi Mark

I also brought a Ajax aj8 about a month ago if you look on my posts new toy and latest engine

mine is a bench top model with a splash tray witch the mill is bolted to it I would be interested to know the pulley set up on yours and their sizes

mine came with a mod with extra pulleys have put it all back to the original set up but doint known if the rpm is right its working ok it also came with a vertical head attachment

I have made a new arbour bearing and end mill holders to fit instead of the arbour so I can mill with end mills horizontally

when I was an apprentice in the toolroom we had a powered hacksaw the top casting had been cold stitched

and worked fine

if I can help please shout Geoff

Mark Davison 121/03/2018 17:38:37
58 forum posts
14 photos

Geoff, I have that model too ! This one is in addition for now, although I will have to sell one as I don't have room for both). Like yours my bench top one had been modified and I've put it back to as near standard as I can (I can't find any photos of one that hasn't been modified). I think they all get modified to reduce the speed to enable use of 6" cutters. This AJ8 appealed partly because the footprint is smaller as the motor is mounted in the pedestal and I'm tight for space, but also because it looks like it has more vertical capacity (although I haven't picked it up yet so can't be sure). This one also has a Morse Taper socket for the arbor so I can add an ER32 Collet chuck and run an end mill. My bench mounted seems to have a proprietry socket.

geoff adams21/03/2018 17:51:48
130 forum posts
144 photos

Mark

mine has .75 dia location spigot and 1" across flats drive to fit the spindle

Geoff

Mark Davison 121/03/2018 18:06:32
58 forum posts
14 photos

This is the end of the arbor on my bench mounted one. As you can see it is quite substantial. I have seen photos of your set up before, but never this one.

 

 

20171105_220128.jpg

Edited By Mark Davison 1 on 21/03/2018 18:12:55

Samsaranda21/03/2018 18:25:19
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794 forum posts
5 photos

Muzzer’s suggestion seems to be the most logical, the crack isn’t going to go anywhere it’s effectively stop drilled at each end because it runs from a free edge at the access panel to near another free edge at the lower end. Filled with an epoxy filler and painted over during the refurb and it should give no more trouble.

Dave W

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