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Repair required for Milling Knee

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Nicholas Hill05/09/2019 12:32:07
25 forum posts
14 photos

Hello,

I recently bought an old Ajax Horizontal Milling machine, unfortunately, the owner knocked it over while loading it...this broke the handle off the bed screw, and also, more crucially, the dovetail of the knee cracked off.

I have looked into getting it welded, but a local company is quoting £450....for about 3 inch of welding...This seems very expensive, considering the machine is only £50 (the owner gave me a hefty discount after his accident). Has anyone any suggestions of good cheap cast iron welding service? Or an alternative option? I have thought of drilling and tapping, but am not convinced there is enough material.

I have attached some pictures, to give an idea of the problem.

ajax_crack2.jpg

ajax_crack1.jpg

Many thanks in advance for any help, or suggestions,

Nicholas

HOWARDT05/09/2019 12:52:56
466 forum posts
14 photos

Machine both pieces and add a piece in between, use a tenon and slot to give some sort of positional key, and screw together. Obviously the assembly will need licking up to get is all true again. Alternatively can you machine it and add a new plate and nut bracket, obviously this would move the other slide dovetail further out, but may give you more material to bolt into and taper pin to retain position.

Ian Parkin05/09/2019 12:55:11
avatar
665 forum posts
174 photos

Well i would clamp it together and assuming that the parts fit well together drill and bolt it with about 4 m8 or m10 bolts if you can get them in

use it and look for another machine to use for parts

i weld cast iron regualrly but thats a difficult one would need machining the dovetail after welding

Juddy05/09/2019 13:04:08
avatar
63 forum posts

I would glue that back together then fit a thick plate on the back drilled and tapped from the bottom, or mill the edge flat and make a new dovetail with an additional 'L' shape to allow attachment to the back by drilling & tapping, you could also drill into the edge and fit dowels in both cases.

Tony Ray05/09/2019 13:04:11
137 forum posts
10 photos

What a shame, I always insist on payment before the purchaser starts moving the machine. the move is their responsibility even if I am helping them.

If you look at Keith Rucker channel Vintage Machinery on YouTube he prefers to braze cast iron as do others.

If that's not an option this is what I would do

Thoroughly degrease the fracture surfaces - brake cleaner is good.

Apply high strength superglue or epoxy it need to be thin so it can flow out of the joint when you compress it, having the part at 40 C will help.

Clamp it if needed ensuring there is no distortion.

When fully cured drill and tap, looking that the part I would choose a thread that is no more than 1/3 of the width of the joint. choose a tapping drill that is a little larger than recommended and use a new tap. If you can, go 10mm into the other half of the joint. don't bottom the tap out as the force may disturb the bond line.

Use the brake cleaner to degrease each hole then remove all swarf.

Choose machine screws that are longer than required, apply high strength retainer and screw them in. when fully cure cut off the excess thread and file down to a neat repair,

If you can add a reinforcing plate anywhere that will help

Brian Oldford05/09/2019 13:10:59
avatar
582 forum posts
4 photos

+1 for the brazed solution for cast iron. Welding will almost always result in the formation of brittle carbides are the edge of the weld.

IanT05/09/2019 14:38:58
1357 forum posts
137 photos

Yes, it could be certainly be brazed (SIF bronzed) Nicholas

I had an old cast-iron Myford countershaft that was badly cracked and it was brazed by my then (welding) Instructor at evening class several decades ago. That was a good 6" crack in a much lager assembly. I think he heated the surfaces to red-heat & then cooled them before actually fluxing, reheating and applying the braze (but it was long time ago). Possibly to burn off the surface graphite content?

You might also want to consider drilling and threading the parts so you can bolt/hold them together whilst brazing it - my guy used Oxy/A to do the work of course but I suspect there may be other (possibly more primitive) methods available too.

IanT

Harry Wilkes05/09/2019 14:51:56
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729 forum posts
60 photos

Had a similar repair to do during my working days I drileed and tapped one half and bolted it back togather then for good measure had my welder braze it up as well,

KWIL05/09/2019 14:52:03
3129 forum posts
57 photos

I think I would have left it where it lay, in pieces and still having the £50.

Mike Poole05/09/2019 15:46:39
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2185 forum posts
52 photos

This may be a candidate for a stitch type repair, this is done by some repair workshops. Google may bring up somewhere near you.

Mike

HOWARDT05/09/2019 16:41:44
466 forum posts
14 photos

+1 stitch repair. Forgot about this have seen it used in the past for both full break and crack repair. Google it, a few companies about who specialise in this.

Nicholas Hill05/09/2019 18:09:53
25 forum posts
14 photos

Many thanks for all the advice. My first thought was to bolt it back together, but had heard that welding was an option. But at the price quoted, I am now, based on the replies, reconsidering screwing it together.

The piece is approx 12mm thick, so based on the above post, should I only use 4mm screws, or can I go larger, as 4mm seems a bit small.

How does the strength of the joint compare to a brazed one? Would a screw and glue method be sufficient for basic hobby workshop use? Or is it more of a stop gap solution?

As for the idea of dumping it....when I was stripping it yesterday, I totally fell in love. It is beautifully made, everywhere you can see the thought and design. The knee is raised by a series of bevel gears on a threaded rod. The feed screws are secured with tapered pins, not peened pins. You only need 3 allen keys and one spanner for everything. Besides, apart from these....minor issues...it is a good honest machine.

As my previous pictures don't show the full glory, this is how it arrived yesterday.

ajax_all.jpg

Many thanks again, for the suggestions,

Nicholas

Brian Oldford05/09/2019 18:33:00
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582 forum posts
4 photos

It's probably complete junk. Send it here for safe disposal. wink

Edited By Brian Oldford on 05/09/2019 18:33:18

Howard Lewis05/09/2019 18:42:51
2439 forum posts
2 photos

If you are in love with the machine, and are REALLY confident of your ability to give it the TLC needed, go ahead.

Having done drilling and tapping bit for a backing plate to hold the two bits together, I would feel inclined to coat the fracture face, and the faces of the bits in contact with the backing plate, with an anaerobic sealant, before clamping the faces together, and tightening the M4 or M5 screws, (My preference, for greater strength ).

If successful, you could finish up with a really useful machine, that eventually, you wonder how you ever managed without it.

Howard

old mart05/09/2019 19:40:06
775 forum posts
76 photos

I would clean the broken parts and degrease them, the fact that the break is fairly straight and square means that the parts can be clamped together with g clamps. Then drill and tap for 6mm about 12mm from each end. A clearance hole through the outer part and about 3mm deep in the inner part before the threads start. Use the clearance hole to hold the tap straight, and you may need to unclamp the parts to get the tapped hole deep enough. You need at least 12mm of thread length in cast iron, more if the taps will reach. When the first two threads are finished, screw in a couple of SHCS high tensile (12.9) and you can remove the clamps to allow more 6mm screws at about 14mm spacing centre to centre. Finally degrease the parts and assemble with epoxy resin across the break.

You should be able to get at least 6 screws in that length, more if possible. It looks like having the screw heads with thick washers sticking out will not get in the way of anything, this is preferable to counterboring them flush.

Neil Wyatt06/09/2019 17:25:03
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Moderator
16738 forum posts
689 photos
76 articles

Only 3" high?

Glue it together. Fill the holes, add 1/8" of depth to the working surfaces and use it as a pattern for a new casting.

Edited By Neil Wyatt on 06/09/2019 17:25:23

Mark Davison 106/09/2019 20:34:08
57 forum posts
14 photos

I have two of these, the same English made bench version you have pictured and a floor standing import. The import had a cracked main casting when I bought it (pics in gallery). Personally I'd glue, drill and tap. It you still want to braze it at a later date you could. If the braze goes wrong now the knee will be scrap.

Robert Atkinson 207/09/2019 08:47:24
avatar
398 forum posts
21 photos

+1 for epoxy and threaded fastteners. Ideal would be low head shoulder type like this

https://www.accu.co.uk/en/ultra-low-head-socket-shoulder-screws/50351-SSHUL-M4-4-A4

with the shoulder crossing the break.

I'd sort out clamping, and possiblr drilling jig, throughly clean mating surface, uses quality slow cure epoxy and about 40 deg C heat. Leave for a couple of days then dirill threading holes an clearance in small part for standard screw. thread and bolt with standard screws statting ain to places and screwing up before drillin next. On last hole after tapping drill, ideally ream, and counterbore the hole for the shoulder bolt. Clean hole and assemble bolt with permanent anerobicthreadlock / bearing retainer (loctite). The move to the most distant hole, remove screw and drill /ream/counterbore for bolt. untill all done. If the counter bore / head is wider then the dovetail just machin back after allowing 24 hours for loctite to set.

Robert G8RPI.

Clive Foster07/09/2019 09:40:37
1885 forum posts
59 photos

On a similar issue, maybe 30 years ago, I was advised to use the highest strength Loctite engineering adhesive with the appropriate primer rather than epoxy. Lasted over a decade to my certain knowledge. As I recall things the adhesive was around £20 a bottle back then!

Loctite was said to give a thinner glue line and, being a factory made single part adhesive, more likely to achieve its stated bond strengths. Epoxies have to be mixed before use. Its quite difficult to get an exact and even mix for small quantities. Especially in the home workshop where you don't have the proper mixing equipment. Generally the epoxies sold for home and small quantity use are more tolerant of minor mix variations than the full on industrial breeds but they do tend to be weaker and, often, prefer a slightly thicker glue line. As epoxies thin out when they warm up during the setting process you can have flow issues with the stuff trying to run out or leaving voids.

I have seen failed epoxy repairs having very uneven glue lines with voids and obvious area where bonding was not achieved on both sides of the joint.

Engineering cyanoacrylate glues are just so much easier to handle. On a cast iron break the surface area is huge so bond strength isn't really an issue save for the usual impact in tension and peel strength weakness characteristic of pretty much any metal to metal adhesive bond. Small screws are fine as they don't take any significant amount of pure load. Just there as anti-peel and impact crack stoppers.

Clean rotary wire brush then liquid cleaner as advised by the adhesive maker. At teh stronger end of the market the cleaner often has priming properties helping bond strength.

As ever with glues good technique usually trumps theoretical higher strength.

Clive

 

Edited By Clive Foster on 07/09/2019 09:43:04

Baz07/09/2019 10:04:52
269 forum posts

I think I would first off go and have a chat with the local foundry and see if they could use it as a pattern to cast a new one, then explore brazing it back together.

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