Author Topic: Banjo Build  (Read 153816 times)

Offline vtsteam

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Re: Banjo Build
« Reply #125 on: June 10, 2015, 11:53:45 AM »
Simon, warping is almost always the result of uneven heating or cooling. One side increases in length from heat while the other possibly more or less plastic does not change at the same rate. When they cool, they are different lengths, and so, curved. So heating all over evenly is pretty much the way to avoid it.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline S. Heslop

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Re: Banjo Build
« Reply #126 on: June 10, 2015, 01:19:57 PM »
That makes sense.

I've got a new problem now, I can't make a chisel/ punch that will hold an edge. Even went back to the HSS toolblank but it didn't take long for the tip to chip off. I'm wondering is perhaps the file is harder now than it was before.

Offline vtsteam

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Re: Banjo Build
« Reply #127 on: June 10, 2015, 02:31:18 PM »
If it cooled rapidly, yes.

Also a lathe toolblank is not designed for impact like a cold chisel is. Start with a re-ground cold chisel and that will work better. You can use silver steel (drill rod) too but you need to harden first and then temper back down to a level that can be used as a metal chisel. Otherwise it will be too brittle.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline S. Heslop

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Re: Banjo Build
« Reply #128 on: June 10, 2015, 03:04:18 PM »
If it cooled rapidly, yes.

Also a lathe toolblank is not designed for impact like a cold chisel is. Start with a re-ground cold chisel and that will work better. You can use silver steel (drill rod) too but you need to harden first and then temper back down to a level that can be used as a metal chisel. Otherwise it will be too brittle.

I was using some drill rod and just went back to the HSS toolblank after the drill rod didn't work. I'm not really too excited about that drill rod though. I've used it in the past and I felt it was somewhat soft even after hardening. Maybe they sold me the wrong stuff!

One source of pretty good hardenable steel i've found is motor spindles. I think I might still have one hanging around somewhere. I could perhaps use the one out of that drill I wrecked a month or so ago.

Offline S. Heslop

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Re: Banjo Build
« Reply #129 on: June 10, 2015, 04:44:59 PM »


I made a nice chisel from a motor shaft. Got it hardened (the little gouge on the right was from a good few mighty strokes with a round file, it's maybe not as hard as it could be but it's still pretty hard). And the end got dulled after a couple of taps, and it didn't raise any teeth.

I think i'd conclude from this that the file is still harder than it should be. But if blocking the ends of the firebrick forge wasn't enough to let it cool slowly then i'm not sure what would be. Or rather, i'm not sure what would be practical for me.

I might maybe try running the metal melting furnace and putting the files in that, and blocking it off to let it cool. It's not hugely insulated though, using just dense refractory, and it'd use alot of gas doing that.

One other thing I might be able to try is building a long hearth out of firebrick with a coal or charcoal fire inside, and letting the files cool down inside of that.

Offline vtsteam

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Re: Banjo Build
« Reply #130 on: June 10, 2015, 04:50:42 PM »
Put them hot into a bucket of wood ashes. It's perfect insulation for this kind of thing. They'll cool slowly to annealed state.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline awemawson

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Re: Banjo Build
« Reply #131 on: June 10, 2015, 04:56:47 PM »
Concrete 're-bar' hardens nicely as a chisel in most cases, unless it's Chinese and made from melted down Twin Towers !
Andrew Mawson
East Sussex

Offline S. Heslop

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Re: Banjo Build
« Reply #132 on: June 10, 2015, 04:57:55 PM »
I remembered reading about people putting them in buckets of sand, etc. But being fairly thin I imagine they'd lose alot of their heat to the sand as soon as they're put in.

So when you say wood ashes do you mean hot wood ashes? I've got alot of wood scraps that I still need to get rid of. Also should they be glowing before putting them in the wood ashes/ fire or will the wood fire be enough to heat them up?

I did look this stuff up a while ago but I just found a bunch of junk about knife-making. I think 95% of people playing with hot metal are making knives. I'm not sure if i'll ever understand the appeal of knives.

Offline S. Heslop

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Re: Banjo Build
« Reply #133 on: June 10, 2015, 05:02:11 PM »
Concrete 're-bar' hardens nicely as a chisel in most cases, unless it's Chinese and made from melted down Twin Towers !

I'm still keeping my eye out for some of the stuff, but despite being apparently ubiquitous i'm having a hard time finding any. I suppose a builders merchants might stock some but they also probably sell them in considerable lengths/ quantities.

I guess any time there's demolition going on of something that'd be full of rebar they'd tend to block the sites off.

Offline awemawson

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Re: Banjo Build
« Reply #134 on: June 10, 2015, 05:02:28 PM »
I'm not sure if i'll ever understand the appeal of knives.

Well said that man !
Andrew Mawson
East Sussex

Offline awemawson

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Re: Banjo Build
« Reply #135 on: June 10, 2015, 05:04:27 PM »
PM me your address and I'll send you some off cuts
Andrew Mawson
East Sussex

Offline S. Heslop

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Re: Banjo Build
« Reply #136 on: June 10, 2015, 06:46:00 PM »
PM me your address and I'll send you some off cuts

That'd be fantastic, thanks.

Did a bit more looking for file stuff and found this video where a guy dunks it into a bucket of vermiculite.



I think I remember Wilkinsons stocking bags of the stuff. I don't really have enough wood ashes to fill a bucket. I'm still not wholly convinced on the idea but I suppose it's worth a go.

Offline vtsteam

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Re: Banjo Build
« Reply #137 on: June 10, 2015, 07:39:14 PM »
I remembered reading about people putting them in buckets of sand, etc. But being fairly thin I imagine they'd lose alot of their heat to the sand as soon as they're put in.

So when you say wood ashes do you mean hot wood ashes? I've got alot of wood scraps that I still need to get rid of. Also should they be glowing before putting them in the wood ashes/ fire or will the wood fire be enough to heat them up?

Simon, the wood ashes are just plain (cold) leftovers from any wood fire. They are very light in weight (unlike sand) and highly insulative (unlike sand). We use wood heat here so they are plentiful. I've annealed many times using them, and it is traditional. They are also useful for slow cooling cast iron after brazing or welding to prevent cracking.

Yes you can also use a wood fire for heat to anneal, but you must have a good pile of red hot embers for that (ie. a strong mature fire and strong draft). it is the embers (charcoal actually) that have the high enough temperature. Wood fire flames are relatively cool and won't work. I have used the wood stove to anneal a piece, then plunged it into the ash bucket -- quite handy in winter since they are all normally in one place and indoors.

See my pipe and bolt engine process early on in that Mod-up here on the forum, where I annealed a hard cast iron pipe cap for the crankcase in the wood stove and cooled in wood ashes -- and the result.

Wood ashes can also be mixed with water to make a refractory for lining a forge -- saw that done once on a video, but haven't tried it.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline vtsteam

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Re: Banjo Build
« Reply #138 on: June 10, 2015, 07:58:31 PM »
Speaking of rebar, I just started laying out the cistern base today. Rebar is availabe at practically any lumberyard here, Home Depots, etc. Cost is currently about $5 per 10 foot length of #4 (1/2" dia.). Bought 30 lengths yesteday.

Never tried hardening it for tools....

I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline awemawson

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Re: Banjo Build
« Reply #139 on: June 11, 2015, 04:21:58 AM »
Simon,

A couple of bars are all wrapped up and being collected by MyHermes on Friday - should be enough to make four chisels
Andrew Mawson
East Sussex

Offline S. Heslop

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Re: Banjo Build
« Reply #140 on: June 12, 2015, 08:34:47 AM »
Take two.


Reshaped forge worked quite well. Perhaps could've been a bit longer where I stick the metal in, to cover more of the file. And ideally i'd have blocked more of the end where the burner goes since it was fairly open and had a bit of a flame coming out of it as well.


The vermiculite i'm not so excited about though. Gotta let it cool, but there's a fair amount of steam coming off of it, which i'd sort of expected after reading the packet and it saying something along the lines of 'ideal for absorbing water'. The bin also sprung a leak out the side where the heat from the file made it about.. 5cm? It's a short distance but it happened fairly fast.

So i'd be surprised if it works. Plan C will be to build a sort of tall furnace from either sheet metal or something like a bit of pipe (ducting perhaps?). Then make a plaster of paris/ vermiculite lining, fill it with charcoal, send air in via a vacuum cleaner, and let the files heat up and cool down inside of that.

I'm also considering giving this up and just buying some rasps. I sort of want to save the sheet metal for another stupid idea I had.

Offline vtsteam

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Re: Banjo Build
« Reply #141 on: June 12, 2015, 08:53:03 AM »
Simon, for holding ashes, think metal bucket, as in galvanized pail, or garbage pail or large gallon (or metric equivalent) size commercial tomato tin. Or gallon paint can (though these are increasingly being made in plastic here). 5 gallon roofing compound tin. Propane tank. Anything discarded that's metal and round. Fire extinguisher......yes?

Vermiculite will work, not as well as wood ashes, but must be completely dry -- otherwise you're making steam, which process rapidly absorbs heat.

There is nothing wrong with your bricks for a furnace -- or forge, you don't need metal lined with plaster of Paris (unless you want to do that as a project). You could also mortar your bricks together with plaster of Paris and sand, using relatively little plaster and make a more permanent forge or furnace.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline S. Heslop

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Re: Banjo Build
« Reply #142 on: June 12, 2015, 09:02:09 AM »
I was thinking about welding a couple of galvanized buckets together. Mostly I need the height.

Drying and keeping the wood ash/ vermiculite dry is a problem though. And with my current space constraints i'm half expecting to throw the stuff out once i'm done with it.

The idea with the charcoal forge/ furnace is just to let the files cool down slowly as the fire itself dies out. Whatever I build might not even need to be lined with refractory, i'm just trying to think of uses for the vermiculite. If I build something nice I could disguise it as a garden ornament. Some sort of tall square tapered thing with some planters on top.

Offline vtsteam

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Re: Banjo Build
« Reply #143 on: June 12, 2015, 09:10:15 AM »
Well, do you have over there a 10 gallon (metric equiv) galvanized steel dustbin with lid? That is tall, can be kept outdoors and will keep anything inside dry.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline awemawson

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Re: Banjo Build
« Reply #144 on: June 12, 2015, 09:31:52 AM »
6" clay or iron drainage pipe would work, but why can you not just let them cool in your forge - I doubt it'll cool fast enough not to leave them soft ?
Andrew Mawson
East Sussex

Offline S. Heslop

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Re: Banjo Build
« Reply #145 on: June 12, 2015, 10:13:40 AM »
6" clay or iron drainage pipe would work, but why can you not just let them cool in your forge - I doubt it'll cool fast enough not to leave them soft ?

Yeah it surprised me when it didn't work because that's what I tried the second (I think?) time.

Also I think the problem with moisture isn't things getting literally wet, but them absorbing water vapour. The vermiculite was dry to the touch but still gave out a surprising amount of steam.

Also also I took one of the files out the bin and touched the tip of it into some water, and it seems to still be above at least 100°C after an hour. So it's at least cooling faster than in air.

Offline vtsteam

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Re: Banjo Build
« Reply #146 on: June 12, 2015, 11:28:41 AM »
Quote
For most tool and high speed steels, the annealing temperature is about 1600 degrees F (870 C). The tool will need to be held at that temperature for hours. A good rule of thumb is one hour per inch of thickness with a minimum of 2 hours.

The second stage of the annealing process is a slow cooling process. After the tool has been heated and held at the proper temperature, it needs to be cooled at a very slow rate. Generally this rate is 50-100 degrees F (28-56 C) per hour. This is usually performed by leaving the tool in the furnace, turning off the heat and keeping the door closed. The tool can be cooled in still air after the temperature of the tool falls below 1000 degrees F (540 C). After the tool has reached room temperature, it is soft and able to be machined.

I imagine they're talking about a considerably larger furnace and a sealed one at that, to get that slow a cooling rate.

For me it was easy to just put the part in the wood stove embers and leave it -- I don't think I had it in a full hour, but it wasn't just heating for a few minutes with a torch either. Then bury it in a bucket of wood ashes, which I'm sure cooled very slowly, and were dry.

One nice thing about a solid fuel fire is it will die out slowly, so that's another possibility -- put it in coals, or wood embers, keep it hot for awhile, and then let the fire die out naturally around it,. It will likely be covered in ash as well. Seems like a natural for the barbecue, if you have one.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline vtsteam

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Re: Banjo Build
« Reply #147 on: June 12, 2015, 11:55:35 AM »
A lot of good info on annealing high carbon and alloy tool steels here:

http://www.anvilfire.com/article.php?bodyName=/FAQs/heattreating.htm

looks like it might have to be VERY slow cooling, depending on what alloy you happen to have.

The one surprising point in your case Simon is that you seemed to succeed in making the blank soft the first time since you were making rasp marks in it easily. So the question is why, and what changed? Diffrent blank?
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline S. Heslop

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Re: Banjo Build
« Reply #148 on: June 12, 2015, 11:56:27 AM »
Yeah the vermiculite didn't work. We do have a barbecue but it's fairly shallow. But I did notice that my grandad has acquired a real giant charcoal bbq, the half a drum type. 

I also noticed that the files just barely fit into the metal melting furnace, with the tips of the tangs poking out through the hole in the top. Perhaps I could do something with that. I think I remember reading that a tangential inlet doesn't work so great with charcoal but perhaps a strategically placed bit of firebrick might help direct the blast.

Offline S. Heslop

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Re: Banjo Build
« Reply #149 on: June 12, 2015, 12:02:05 PM »
A lot of good info on annealing high carbon and alloy tool steels here:

http://www.anvilfire.com/article.php?bodyName=/FAQs/heattreating.htm

looks like it might have to be VERY slow cooling, depending on what alloy you happen to have.

The one surprising point in your case Simon is that you seemed to succeed in making the blank soft the first time since you were making rasp marks in it easily. So the question is why, and what changed? Diffrent blank?

The first time I heated it up red, then stuck it into the embers of a dying wood fire. Half the file was still poking out though since the fire wasn't big enough.

Plus I was using high speed steel to punch those marks, so that might've helped. The stuff i've been trying to make punches from does harden, but it can still be (just barely) filed. So it's not as hard as it should be. I also tried grinding a bit into that steel to make sure I wasn't just filing off a decarburized layer. Hopefully Andrew's bits of rebar will work better when they arrive.

Y'know it'd probably be diligent to try the high speed steel again. I had the tip snap off (which is to be expected) trying to punch it after the first hardening-steel chisel didn't work, and I never tried it again.