Hit a hard spot in a casting; what to do?

[smfr]

Happy Christmas everyone! Here's a Christmas conundrum.

I just hit a hard spot in a Stuart Beam valve cover casting, while drilling a #37 hole. I tried chucking up a stiffer center drill and going at it with that, but the drill isn't going anywhere

So I'm wondering what my options are. Spring for a solid carbide drill? Try to find some kind of diamond-tipped Dremel tool that's thin enough? Try drilling from the other side and hope for the best?

Thanks!
Simon

 

[steamer]

I would try with a carbide drill. That usually makes short work of hard spots.

Dave

 

[Springbok]

Hi
Have had this problem in the past with hard spots in castings found my biggest problems were with 7.25g Hunslet train wheels. especialy when turning. The hard spot is normally only extremely thin and when you break through all will go well try a spot drill to start with excuse the pun and break through the few thou. There has been a lot written about this subject over the years. and there has been so many opinions you could start a book but it is down to the individual foundry and dare I say it the person pouring the metal.

Have a prosperouse New Year and lots of fun in the workshop

Bob

 

[Ramon]

Hi Simon, Carbide will normally sort out a hard spot problem but beware if the hole is situated half and half so to speak. The one thing carbides don't like is any kind of flexing - well didn't when I was using them at work but that is a few years back.

Another approach - if you are able to, now that you have it machined - is to heat it up to a nice bright red going on orange and bring the temperature down as slowly as possible - the longer the better. Of course it will discolour it again but if it's going to be painted that should not present too much of a problem. Hard spots are a pain at any time but at least with this small item you should be able to do the above without too much hassle.

I don't know if you've seen it (on the table engine thread) but have just done something similar with ballbearings and though still tough it worked fine using HSS drills.

Hope this is some help.

You are doing a fine job so far - you must be getting close to a run

Regards - Ramon

 

[d.bick]

Cast iron castings that has been removed from the sand whilst still near red hot can have chilled areas or foreign steel items can find there way into the metal during the melting process causing hard spots.
A friend of mine stated he chose the best grade of cast iron the foundry had. On hearing this another friend Larry pointed out he probably had what ever was in the pot at the time. Larry told me always look at the scrap pile at the foundry, we did this at a local foundry and found a gearbox complete with gears and bearings ready for the next melt. As stated in a previous post heating to red with a slow cooling period will soften the hard spots this can be done in a fire over night
Dave Bick

 

[coopertje]

Hi Simon,

I am building a Stuart 10H at the moment and I am fighting with the same issue. Normally the hard spot is thin, but in my sole plate its not. If I can reach with carbide (and when I have the correct size on hand) it goes through like butter. I tried to heat and cool down the casting without success. This week I have milled down a complete part of the casting to get rid of the hard spot and silver soldered a piece of metal in place....

Good luck with your restoration, your work is outstanding! :bow:

Regards Jeroen

 

[Jasonb]

Another vote for heating it and letting cool slowly, had this problem several times in my IHC Famous thread. Either leave it in a fiore for a few hours and let cool in the ashes overnight or blast for 10mins with a propane torch and leave on teh hearth to cool.

As its only the valve chest cover you could just bin it and use a bit of 1/8 plate or flat stock.

J

 

[Ramon]

Just like to add a bit more on this - it's not so much the heating - give it a good 'soak' by all means but it is not the length of the heating but more the cooling period that does the trick. The longer it can take to cool from red heat the better. Obviously depending on the part this can prove a problem - Jeroen's base for instance with all the previous work done but as Jason says leaving it to cool in a fires embers is probably the best option to achieve this that most of us have access to. Theres always charcoal and a BB of course


Let us know how you get on Simon.

Ramon

 

[steamer]

Ramon is correct. Slow cooling is the key. It also depends on what's available for equipment. I recommended the drill over the heat as I didn't know what Simon had for equipment. If you've got a way to heat and more importantly to cool it slowly, go for it. I would second that with that point that if your going to run this on steam, softening the cover is a good thing.

Dave

 

[rkepler]

A hard area on a thick casting is likely to be relatively thin, but a hard spot on a thin casting is likely to be all the way through. On the former I just slow down and go at it with sharp carbide, on the latter I run the casting through the heat treat oven for a run at 1425-1475 degF. You'll lose a grade in the cast iron (class 40 will go to class 30) but usually something like a valve cover isn't subject to any real stress and the lower grade doesn't matter.

 

[mcostello]

Just as an aside a local foundry had a delivery made with a semi and mentioned cast iron was going for so much a ton. Truck driver said that if he could get that much a ton for his truck he would sell it. They said take fuel tanks off and drain fluids snd they would buy it. He came back with another truck and drained everything and sold it. It went into the pot and this was a cast iron foundry supposedly no steel. Maybe you hit a piece of hydraulic lifter left over.

 

[smfr]

Thanks for all the suggestions, folks. Alas I don't have a hot enough torch, or a hearth to do heat treatment in. Shouldn't have dismantled that brick barbecue in the garden all those years ago

I have some carbide bits on order from Enco, so we'll see how those do. I fear I might be on the edge of a spot, because the drill was going off to the side. If the carbide doesn't work out, I'll just make a new cover from stock.

 

[Jasonb]

If the dril is getting pulled off line then drill a hole in say a bit of 1/4" flat stock and clamp that over the hole to guide the drill bit

|You could also plunge cut with a carbide slot drill

J

 

[bearcar1]

Maybe drill it oversize, plug it and then drill as you would normally do? Just a thought.

BC1
Jim

 

[flatbelter]

If you have a self cleaning oven you can throw the part in and run it through a cleaning cycle.

Otherwise, I heat with a torch to a dull red heat, then bury it in dry sand to cool.

 

[rkepler]

If you have a self cleaning oven you can throw the part in and run it through a cleaning cycle.

It's got to be a heck of an oven, mine certainly doesn't break 800 degf, maybe 1000. When I first had to do this I cycled the cast iron at 1200, 1350 and finally at 1450 (IIRC) before the chill would go away. To me 1450 is getting up into the "cherry red" temperature.

 

[Dan Rowe]

For those that do have an oven or burnout kiln that can achieve the temperatures needed what would be the best cool down ramp?

I run my flasks to 1350 deg F all the time but I would have to program a cooling cycle as I usually just ramp down to 900-850 deg before a lost wax pour.

Dan

 

[purpleknif]

Just a note on the carbide drills. As a full time machinist I've run into my share of hard spots, sand pockets, and broken taps. Most guys try to use a high rpm with carbide. I have had a lot more success using a slow rpm and a very fine, usually hand feed. Think shavings, not chips.

 

[rkepler]

For those that do have an oven or burnout kiln that can achieve the temperatures needed what would be the best cool down ramp?

I don't recall running anything really unusual. Probably I set it to 100 degF/hr and shut things down at 1000 degF. Once it's below the critical temperature (1200 degF?) things aren't going to change with the speed of cooling. But this link suggests that there are multiple causes for what we call "chills" and possibly multiple solutions:

http://www.keytometals.com/page.aspx?ID=CheckArticle&site=kts&LN=EN&NM=112

The problem in finding this sort of information is that in an industrial 'production' environment you'd just scrap the casting and have a new one made properly in preference to trying to machine through it or heat treat it; that and the deliberate production of chilled cast iron means that decent heat treat info to remove chilled sections is hard to find.

 

[lordedmond]

If you purchased these casting , send them back for replacement , hard spots/ blow holes are faults and should be replaced by the supplier

if they get a lot back they may do something about the quality


Stuart