Cast iron bed crack - options

[jimi]

Hi Don, I have been doing NDT or as you call it crack detection work for the past few years and to detect a little better the cracks you normally use a white contrast paint before applying the black particles mixed with kerosene , this way they are free to move around to the crack. you normally do it without contrast paint when it is hot, then you use what they call a pear to sprinkle the powder on and this is red to contrast with the dark metal background (the particles are very fine). Before they used liquid penetrants like you see today, they would apply oil, let it penetrate a while then clean the top surface only lightly to get rid of the oil on the surface and then apply chalk powder. if any dark areas appeared that would be a sign of the chalk absorbing the oil from a crack. If you are going to be doing this often i would look for a can of dye penetrant, 1 of cleaner and 1 of developer this way you will find very fine cracks as long as you execute it properly. If one day you do it, let me know. If you keep doing your magnet method, move them around as the cracks could be orientated at a different angle to the magnetic field you are applying (normally 90º to the first position). Hope this helps, Regards jimi.

[DonInReno]

On 10/26/2018 at 2:13 PM, chrisash said:

Probably very nieve but could you not put some baces screwed into the clear sides of the split on either side...

I ran into something unexpected that relates back to your question.  After grinding out most of the crack and clamping it to some thick pieces of 4” angle as the slight bend straightened the original crack in the web on either side closed up before the bed straightened completely - it was only about half way to straight.  About .040” had to be removed - the webs were stretched a little before they gave out.  

 

On 10/27/2018 at 3:18 AM, jimi said:

Hi Don, I have been doing NDT or as you call it crack detection work for the past few years and to detect a little better the cracks you normally use a white contrast paint before applying the black particles mixed with kerosene , this way they are free to move around to the crack. you normally do it without contrast paint when it is hot, then you use what they call a pear to sprinkle the powder on and this is red to contrast with the dark metal background (the particles are very fine). Before they used liquid penetrants like you see today, they would apply oil, let it penetrate a while then clean the top surface only lightly to get rid of the oil on the surface and then apply chalk powder. if any dark areas appeared that would be a sign of the chalk absorbing the oil from a crack. If you are going to be doing this often i would look for a can of dye penetrant, 1 of cleaner and 1 of developer this way you will find very fine cracks as long as you execute it properly. If one day you do it, let me know. If you keep doing your magnet method, move them around as the cracks could be orientated at a different angle to the magnetic field you are applying (normally 90º to the first position). Hope this helps, Regards jimi.

That’s all useful information!  In fact this morning just as I was about to start preheating the bed prior to brazing I noticed a faint line that wasn’t there the night before - apparently it was oil that had migrated down into the crack and some dust had collected on it overnight and in daylight it really stood out.  I ground down another 1/16” to 1/8” to remove what was obviously more cracked material.  

The old advice to go slightly past the point where the crack stops and drill a hole to prevent further cracking makes sense to me now - the crack extends further into the material than can be seen by naked eye.  I’ll almost bet the bed on my machine has micro cracks clear through it - if not from the original damage, from me clamping it straight while cold.

On 10/27/2018 at 12:06 AM, carlcarl said:

 I’d still preheat (I bought a used gas bbq just to use as a preheater!) 44-30 can be filed or ground if you want to clean it post weld.

I’m also a fan of brazing cast iron, but I haven’t done any of that since I bought a spool of the 44-30.  

Best of luck

Carl

 

After brazing this bed I’m definitely going to look into welding the next one.  I have a cheap inverter dc tig setup and will probably upgrade to another TIG.  It’s funny how the cost of nickel TIG wire is definitely less than the amount of gas I used today.

I was out of propane for preheat and the #4 gas tip really took a long time and probably wasn’t large enough for the deep grove on the three sided inside corner (the pic showed the spot when I first started grinding, but the grove ended up being almost the entire thickeness of the bed and undercut the leg quite a bit.  I was about to grind it out and TIG braze it while everything was still hot but the batteries in my auto dark helmet were weak enough to flash me so I said screw it, wrapped everything up and came inside. Lol

For preheat I’ve always used a propane weed burner and have a couple of fiberglass welding blankets to wrap and conserve heat for post heat but a dedicated gas bbq would be nice especially to burn off oil and paint - I’ll keep an eye out for one! 

 

[brmax]

It looks and from the conversation, the project is moving right along. Good work!

In some other future task like that, especially cleaned up as that is. I found great use from a typical oven. They have seriously helped me in cast welding items that fit. 

Many have a clean cycle, it gets a nice hi temp good for preheat. Along with another application for after weld stabilizing with a slow cool down.

These are also great welding rod, keep dry/ heaters also. Just as you mentioned the bbq pits for pre heat, great point!

 

Good day

Floyd

[LederMaschinist]

 

On 10/26/2018 at 11:38 AM, DonInReno said:

That reminds me to stop by the metal yard and buy some angle to keep it lined up during brazing. Lol

It sure looks like you know what you're doing, but make sure the angle is dead straight before you use it to align the bed.  The tolerances the mills use for straightness are nowhere near straight enough for this project.  That doesn't mean they aren't straight, it just means they might not be straight enough.

[DonInReno]

On 10/28/2018 at 9:07 PM, brmax said:

In some other future task like that, especially cleaned up as that is. I found great use from a typical oven. They have seriously helped me in cast welding items that fit. 

Thanks Floyd.  I’ve been interested in an oven for powder coating, but more uses keep popping up.

 

18 minutes ago, LederMaschinist said:

...make sure the angle is dead straight before you use it to align the bed.  The tolerances the mills use for straightness are nowhere near straight enough for this project. 

Exactly - that’s a very good point.  I ended up with a few pieces that were pretty straight and the bed clamped down quite flat, which was encouraging.  However it was a rookie mistake on my part to clamp it dead flat and not allowing for shrinkage of the bronze under the bed.  This morning a quick look with a straight edge showed a few unexpected irregularities in the top of the bed.  The most obvious was due to shrinkage of the bronze - I’m thinking that can be corrected when I go back for round two to fix a few things.   The second surprise was a slight bowing of the bed essentially from the front feet of the bed on back to the area of the crack - originally I had hoped it would be nearly flat other than where the crack was.  If the bed were steel it would be easy to straighten with a torch, but I’m guessing that’s not an option with cast iron.  This second go around I’ll try to get the joint at the crack a bit flatter then lap the entire bed flat so it looks decent.

 

[Northmount]

@DonInReno It helps if you can maintain the same amount of heat on both sides during the welding or brazing process.  Sometimes quite difficult to do.  Slow cooling might help too.  Over 50 years since I did some brazing of cast iron!

Tom

[DonInReno]

On 10/30/2018 at 9:02 AM, Northmount said:

@DonInReno It helps if you can maintain the same amount of heat on both sides during the welding or brazing process.  Sometimes quite difficult to do.  Slow cooling might help too.  Over 50 years since I did some brazing of cast iron!

Tom

Until recently I’ve never spent much effort conserving heat on the backside and opposite end of a project, but a few well placed bunched up welding blankets made a huge difference in maintaining even temperatures.  A good infrared thermometer has really been enlightening during preheat - at least for me it makes the difference between guessing and being within 200 degrees from one end to the other to simply taking a few measurements and easily being within 50 degrees.

The next time I may prop the machine’s bed on its side to go a step further and allow torch access to the back.