Banjo Build

[S. Heslop]

4-in-hand rasp

Oh that's what they're called. It's also interesting to hear that about surforms. I was never too confident in them just from the way they looked. If I remember right they come in a few different teeth shapes, some have sort of arched teeth from being punched down, and others have a fair amount of material removed around the tooth which is then bent down but kept rather straight. The second variety (neat story) in particular never seemed so ideal.

[S. Heslop]

So that big four in hand rasp seems to have gone soft. Or perhaps it was only ever case hardened. I'll probably cut a tang into it and then try hardening the waste to test.

Also I've been wondering about case hardening. Perhaps I could put teeth into a bit of mild steel then try case hardening that. If you're using fancy materials like kasenit (which seems to be sodium ferrocyanide, which I still haven't found a source for but i'm sure it must be available. Perhaps I could contact a chemicals distributor. Or maybe even ask my old university chemistry department) would it be enough to protect the teeth from burning away? The thing of sealing it in a tin with charcoal seems fussy, mostly for the risk of burning a hole in the tin.

I'm also considering skipping the sandblaster part, and going for an acid etch. I think i've read that they used to do them that way before the days of sandblasting.


Finally, i'm also even wondering if the teeth need to be hardened. I'm sure it'd help, but it might be worth seeing how long they'd last if left soft.

[vtsteam]

questions, questions! Only way to find out some of these kinds of things is to try them!

Kasenit does seal to the part being heated so doesn't need a container, and also acts rapidly, but to mainly produce a thin case.

The pack hardening methods are usually used to get a thicker case. The container wouldn't likely be a tin, but something thicker -- pipe is sometimes mentioned -- one end pipe capped, the other just plugged with clay (likely the obvious explosive safety reason). Or a custom made box and lid, also luted with clay.

Kasenit seems to be more than (or other than) sodium ferrocyanide, since it is gray in color.

I've read statements that wood actually can wear tools faster than metal -- source lost to memory, so take with a grain of salt. But best to find out by trying, yourself, I always feel.

I bet the scraps from your 4-in-hand rasp harden when you try them.

ps, can you make a rasp from Andrew's rebar and then harden?

I'm going to still plug for forging whatever metal to shape and immediately burying in genuine wood ashes for a few hours, by way of annealing.

[awemawson]

The original Kasenit used to fuse into a smoothish layer when a red hot item was dipped. The modern stuff seems to have major problems adhering 

[S. Heslop]

I've also heard about wood wearing tools faster. I think i've also heard that bits of sand and grit can get embedded in the wood as it grows, more so in some varieties.

I'm not convinced it does wear tools faster though. Think about a chisel or a plane iron, which are usually just high carbon steel.

Also I did think about making a rasp from the rebar, but I don't think I particularly need a round rasp at this time.


So it seems that making case hardening compound is just gonna be another distraction, and a potentially dangerous one too. Is there any particular go-to variety of case hardening compound? I often hear people complain that the new safer stuff isn't anywhere near as good as the old stuff but I don't think I often hear recommendations.

[awemawson]

The modern stuff works, but you need to keep heating and plunging as it comes off too easily imho.

[S. Heslop]

Sounds like it'd be tricky to do without burning the teeth off.

[S. Heslop]

I'm now wondering about getting some pipe just wide enough to hold the largest file, then welding the end off and filling it with salt, and putting it in that charcoal furnace. Maybe making a ring to support it from tipping over.

Molten salt seems like something that I shouldn't be playing with. Molten metal should at least slide off of skin and clothes, but i'd imagine molten salt would stick to everything. But it's still something i'm considering.

Edit: Yeah forget that. It's too dangerous and i'd be an idiot to try it.

Edit2: I think case hardening seems like something interesting to try. I'm reading more into it. I'll probably do it the traditional way with a sealed(ish) container. I'm just thinking now about how to monitor the temperature so I don't melt anything again. If I can get it to work then it seems like it'd be a reliable way to make rasps from fairly common materials.

[S. Heslop]

So I'm reading that people but bone meal/ bone charcoal in mostly to give it a 'colour case harden'. Almost all the stuff i've found on case hardening has been people trying to turn nice looking guns into marbly messes like this.



I can only figure it became synonymous with 'quality' due to it being at least visually obvious that the thing has been case hardened. Cuz it sure as hell looks ugly.

[vtsteam]

Simon  now don't go messin with gun folks aesthetics. They got their own styles, just like we do -- some like everything in the machine shop gray, some like things green, some go for red, blue, orange, and there's even a guy I know who painted his thickness sander purple! I say go for it, when you build yer own stuff, whatever takes yer fancy. I kinda like the marbeling from hardening -- it's interesting and a bit uncontrolled, which is rare in factory made plastic everything these days!

[S. Heslop]

I understand that people appreciate some weird stuff, but what gets my goat is when certain things become associated with quality. I'm sure you've probably seen some of the horrific bluegrass banjos out there.

In other news, I tried hardening the leftover tang of that rasp and it did indeed harden. I've got the other half of the tang that I might try coating with bar soap to see if it at all protects teeth as it's heated.

I also remembered i've got a big bunch of 50x50x5mm angle iron that would probably make a good canister for case hardening if I weld two halves into a square tube. It'll also be nice to weld something with some thickness for a change. It seems like everything I weld is either tiny or very thin. 

[S. Heslop]

Tried it with a bit of soap and a gas flame and it seemed to do something. It didn't harden as well as the previous bit though, since I didn't let it 'soak' I suppose. Wish I thought to take before and after photos, but it didn't seem to degrade too bad. The two leftmost teeth are snubbed off because I brushed them with another file seeing how hard they got (not very). I also didn't do a great job forming the teeth either.

Trying to get that rebar to harden. Spent a good while whittling that into a chisel shape, roughing with a hacksaw. But it's too chunky to easily heat and I think I jumped then gun on quenching it; hadn't gotten it hot enough.

[awemawson]

Some nice old rasps in this thread on the welding forum - reckon a bit of negotiation might liberate some for you:

http://www.mig-welding.co.uk/forum/threads/worth-80quid.55640/

[Lew_Merrick_PE]

Simon,

>> I think I jumped then gun on quenching it; hadn't gotten it hot enough.

Try using a magnet on a wire.  [I use .004 inch music wire because I use that in a number of other operations.]  A good AlNiCo magnet should draw towards the heating part enough to see while staying far enough away from the heat source.  [Do not try this with neodymium magnets as they do strange things when they get "warm."]  When the steel no longer attracts the magnet, you are (approximately) at the correct temperature for hardening.

[S. Heslop]

I did have a magnet I was using, but it fell into the garden somewhere when trying to anneal the rasps and i'll probably never see it again. Got a few old speakers from a TV i'll probably never use, so I might try borrowing a magnet from those.

[vtsteam]

I did have a magnet I was using, but it fell into the garden somewhere when trying to anneal the rasps and i'll probably never see it again. Got a few old speakers from a TV i'll probably never use, so I might try borrowing a magnet from those.

Well that's the opposite of what usually happens to me -- I drag a magnet around to find a lost steel part in the grass! Can you drag a piece of your angle iron around to find your magnet?

[S. Heslop]

I did have a magnet I was using, but it fell into the garden somewhere when trying to anneal the rasps and i'll probably never see it again. Got a few old speakers from a TV i'll probably never use, so I might try borrowing a magnet from those.

Well that's the opposite of what usually happens to me -- I drag a magnet around to find a lost steel part in the grass! Can you drag a piece of your angle iron around to find your magnet?

I'd need to be probing the bushes because I think it went down the side of the barbecue. I knocked the screwdriver off that the magnet was stuck to, and it fell off of that.

So I still can't get this rebar to harden. Andrew, what do you usually do to harden it? I've been getting it progressively hotter (and past the magnetic point) and quenching in water.

Also I did pick up a cold chisel at a second hand shop. I was thinking about grinding it into a shape for this but it's a bit too long, and it seems like a shame to ruin it. So I ended up grinding it into a shape for cutting metal and honed it to a nice edge. Played around for a bit cutting metal with the thing and it's holding it's edge great, even on steel. I've heard that alot of fitting in the past used to be done with files and chisels, but i've never really understood the purpose of chisels since they more or less do what files do. I suppose they can remove material much faster to rough it out?

[awemawson]

Simon remember that rebar does vary in composition so it is possible that may not harden at all, but it should. Heat somewhat above the curie point then rapid quench in cold water. That will make is as hard as it can be.

[S. Heslop]

It is hardening I suppose, just not hard enough to survive it's purpose. I might try case hardening it too to see how that goes.

Either way, it's a good pair of bars that i'll eventually find a use for. I've been running low on long bits of steel bar.


Speaking of bars, I was spending a while wondering about how I might monitor the temperature while case hardening, to make sure I don't melt through the canister. I was thinking about the expensive and complicated ways, naturally, using thermocouples. Then I realised that I could probably just stick a bit of rod down in the fire and pull it out occasionally to see how hot it is from the glow.

[vtsteam]

Also I did pick up a cold chisel at a second hand shop. I was thinking about grinding it into a shape for this but it's a bit too long, and it seems like a shame to ruin it. So I ended up grinding it into a shape for cutting metal and honed it to a nice edge. Played around for a bit cutting metal with the thing and it's holding it's edge great, even on steel. I've heard that alot of fitting in the past used to be done with files and chisels, but i've never really understood the purpose of chisels since they more or less do what files do. I suppose they can remove material much faster to rough it out?

Yes, they can shear sheet metal held in a vise with a guide, chip grooves, rough down a surface, clean up castings, free steel cores in castings (like my half-nut on the lathe), get in corners you can't get a mill into, cut square where a mill might only be able to do round, split frozen nuts off of bolts and studs, cut off rivets and bolt heads, act as an impact wrench on really big nuts, mark part orientations, etc.

This is a really light treatment, but the best i could find for the moment on the inet:

http://www.appropedia.org/Cold_chisels

[vtsteam]

And found a video, there isn't much out there on cold chisels. Older books and MEs have more  information. I have quite a few cold chisels. Some of the narrower ones are the handiest. It's kinda like hammers. Hard to resist them on a garage sale table, for me at least.

[S. Heslop]

Yeah it surprised me that there's next to nothing on cold chisels on the internet. I feel like any time you see old film footage of a factory you're gonna see more than a few guys using them. Then with the woodworking hand tool scene you'd think there'd be an equivalent for metalwork.

[DavidA]

Re the Poor Man's Milling Machine.

As part of my army training I had to do a plant operator/Mechanic course. This was back in 1969.

As part of that training we did metal work. and during this we had to cut a channel in a steel block to quite close limits using only a hammer, cold chisel,  hack saw and files.
I was swinging mightily with the hammer when someone distracted me and I missed the chisel; But not my hand.
The pain was so intense I nearly fainted (Note,  nearly. Royal Engineers don't faint) . To this day the knuckles on my left index finger are slightly deformed and, particularly in winter, it hurts like hell.

An experience to be avoided where possible.

Dave.

[vtsteam]

It's pretty common to hit your hand, probably because we all tend to use too small a hammer. All too often people grab a household claw hammer to hit a cold chisel with (me included). After enough whacks I've come to instinctively pick a bigger hammer -- the larger the face the less chance you'll miss, and the additional weight is more effective.

You can slow down the hit as well with a heavier hammer, hit less frequenty, which makes it also a lot more accurate in cut. Fast pounding with too light a hammer gets you nowhere, except bleeding. Tapping with a heavier one gives time to adjust hammer aim and tool angle, yet takes off a good chunk of metal with every blow. Of course the hammer size has to be guaged to the size of the chisel.

I don't think a long handle on a hammer helps, and I notice others tend to choke up on the handle where it is  framer length.

If you think about wood chisel practice, there's usually a round mallet or maul with very short handle and good weight, and large hitting area, and you seldom miss, while maintaining good accuracy. I think that also applies to cold chisels, and improvements could be made in what we hit them with.

Some of the usual problems crop up this well meaning video:

[S. Heslop]

I hit my own left index finger knuckle with a big hammer a couple of weeks ago. Right where i'd also hit it with a wood chisel. It's still somewhat sore if I prod it. Seems like that area is the most likely to get hit by stuff! In fact I kept hitting it with that chisel and reopened the cut a few more times till I got the hint. I wonder if those plastic rings you can get for cold chisels to help protect from missed blows are worth it... I could perhaps make something similar from plywood.

Worked on that canister today.


It doesn't look like much but I put a good amount of work into this end cap. I got it fitting just right. Played with the cold chisel a bit more, and i'm not sure if it's just my technique but I felt I could remove material much faster with the half round part of a coarse crosscut file.


Welded. I miss my welding cap and helmet. I lent it to my brother a long time ago and never saw them again, he left them at his old workplace. This handheld visor is pretty rubbish and plenty of spatter landed on top of my head.

Earlier I welded the long seams without the jacket on, just a T-shirt with my arms exposed. I kind of realised what i'd done afterwards but so far i've got no symptoms of arc burn.


The ugliest weld. I went over the lousy first pass at about 120 amps (according to the buzz box) hoping to get some better penetration, but there's still nothing visible on the entire inside of the canister.


The end was equally ugly. I went a bit fast in a few parts (the handheld visor has a very dark shade in it, it's hard to see what's going on even with the arc light) and touched them up.

Time really flied doing all of this. Started at about 10am and it's now almost 4pm. Hopefully i'll have the lid finished by the end of the day. I'm still thinking about what to do, but I think i'll just make two squares and do some plug welds to hold them together, with the inner square (fairly loosely) fitting the inside and the larger square overhanging a bit so I have a corner to shove fireclay into to seal it.

I had a dream last night I was trying to weld in the back of a car. I had nowhere to set the hot metal down so I flung it out the window and started a wildfire. Hopefully it wasn't a premonition!