Re-casting broken saw part

[Pete O]

I've decided to have a crack- so to speak- at casting a replacement component for the giant radial-arm saw that I bought with a broken part. I'll use the broken casting as a pattern. I epoxied the two parts together at the break, then spent a bit of time bogging it up with builder's filler (seems identical to car body filler) to add draft to the machined surfaces and add a bit of machining allowance where it will be needed. Bit of work to do yet before this is ready to ram up in a flask.

Broken casting 2.jpgcasting pattern.jpg

[familyguy]

It looks to be made from cast iron - are you going to cast the new part in iron ?

[Pete O]

It looks to be made from cast iron - are you going to cast the new part in iron ?

Yes that's the plan. I have a broken-up Victoria U2 mill overarm waiting to be melted.

[familyguy]

In your own foundry or are you handing it over someone else to pour ?

[Pete O]

Just my own little waste-oil furnace (who can afford to pay other people to do things?). It will be my first actual iron melt- I've done a fair bit of aluminium and a little bit of bronze but not yet attempted iron. Wish me luck.

I've been mucking about with this casting-come-pattern, I now have it to the point where it will come out of the sand cleanly. I was going to cast it today but ended up having to help a mate with sheep- ugh- and the sand has dried out and will need mulling again. Hopefully tomorrow! Initially I couldn't get the little protrusions on the side to come out of the sand cleanly, I had to fill up the gaps and make it one long piece which will mean lots of material to remove in the machining stage. I'd hate to have to pay myself by the hour for this stuff. Once I've got the casting made, I'm going to have to figure out what will remove all the bog from the original so I can clean it up and copy all the machining accurately. Hopefully some acetone will break down the filler.

[KBs PensNmore]

Hi Pete, the only way I know of to remove a filler like you've used, is by abrasion, wire buff for external and drills/rotary bits for the internal stuff.
From what I've found, is that chemicals etc., may soften it to an extent, but won't totally remove it.
You may have been better off using plastecine or playdough to fill the holes.
HAVE FUN
Kryn

[OxxAndBert]

According to YouTube - solvents don’t penetrate very deep, and heat is the preferred tool.
Hit it with a heat gun to soften it up or sit it on a couple of bars over the furnace after it’s turned off and cooling down.

Steve

[Pete O]

Both of those are good to know, I did some clean up on the wire wheel in between different approaches to the filling and it abrades away very quickly that way but not all of it will be accessible. I applied some masking tape over the holes whose positions are critical, before the filler, so hopefully those will be easily located. Wire wheel, heat gun, drills and taps.

[KBs PensNmore]

For a future reference, you could also turn pieces of doweling (round timber) and force that into the holes, to blank them off.
Kryn

[Pete O]

The first casting attempt is a failure, I didn't get the iron high enough above melt temperature, it was liquid in the crucible but was already returning to a solid state as I started to pour. Only went about half way through the mould cavity. I had the furnace running as hot as I could get it on waste oil, I think I will try adding 50% diesel for the last stage of the burn when I get a chance to have another attempt. I guess if it was easy everyone would be doing it.

[OxxAndBert]

Bugger, but sounds like you were pretty close!

Are you thinking just not enough fuel? So adding diesel will reduce the viscosity and allow more flow?

Steve

[Pete O]

Yeah need to get more fuel burning in the chamber somehow and the furnace designer talks about adding diesel to the oil, probably better calorific value than used sump oil? Not sure. I'll have another read of the design book. The preheat flame was not blasting as hard as it should but I was probably running lean as I got the air feed up full. Bit of a vicious cycle I guess. It's easy to get to aluminium temps but I've got no frame of reference for what works to get it to temp for an iron melt. I was going to reintroduce the propane that I use to start the burn but I decided against it as I thought it was plenty hot. I should probably get a thermocouple so I can do this better. I might do some experimenting just with the furnace before I go through the whole process of conditioning the sand and ramming the mould again just to have a failed pour, it's quite time consuming.

[familyguy]

You're a brave man, good on you for having a go and even more so if you pull it off. Metal casting is something I'd like to have a go at, at least with aluminium, and I will get around to doing it. I've got projects in mind and I could just machine from solid, not only is the idea of starting with a part that has most/all of the waste bits removed quite compelling, but also more complex shapes can be made, like an in line 6cyl model engine.

[Pete O]

From a little further reading of the furnace build manual it seems likely I am not getting enough air from my bouncy-castle blower. I'm going to need to address that before I have another crack at the iron. As mentioned in another thread, I bought a 450watt blower very cheap as I had robbed the motor off my old blower and couldn't find a replacement at a reasonable price. The 450w unit worked a treat for aluminium but probably won't cut it for cast iron. I'm going to have to stop robbing future Pete to pay current Pete.

[OxxAndBert]

Thats a bugger Pete - those jumping castle blowers are are nice convenient package.
If you happen to be over my way I've got a 680W one sitting here that you're welcome to borrow and try. Should flow a bit more air than the 450W.
If you're back to chasing motors for your original blower, old spa pool pumps can be picked up pretty cheaply or free if you keep an eye out. They are often reasonable quality such as Onga or Davey, and usually about 1 to 1.5HP (but I've also seen some 550W ones so be mindful they aren't all the same).

Steve