Did you intentionally leave the lightening holes out of the non-flywheel side bearing mount? Do you think that will push the engine into the over-weight range?
As always, very nice work.
As always, very nice work.
Last edited:
Model Diesel: 32mm bore, 38mm stroke, indirect injection
- Thread starter Nerd1000
- Start date
Help Support Home Model Engine Machinist Forum:
Drat, I knew I was forgetting something haha.
Last weekend's work. I made the last casting I needed, the lower crankcase half/oil pan. This was also my first attempt to run the foundry on liquid fuel not gas, sadly it's also the last for this furnace as the lid has been damaged to the point of exposing the steel reinforcement. The next furnace will need some design improvements to handle the higher exhaust flow, but the ability to run on dirty kerosene left over from parts washing is worth it.
My castings are still a bit rough, but improving. As I plan to paint this engine, I'm filling the rough spots in with high temperature epoxy putty, that's the brown stuff on the part. It's especially important for this one, as i had two pinholes in the thinner areas that would have prevented it from being oil tight. I suspect the cause of these to be inadequate venting of the core. As the core binder burned up the resulting gases pushed through the still liquid casting in the thinnest spots so they could escape.
I then set up to mill the part and get the main surfaces flat and parallel. The hole in the side was left by a chaplet that supported the overhanging part of the core. I was expecting it to melt into the casting (it was also aluminium) but it instead survived and left a very neat opening. That's not a problem, as I deliberately placed it at the eventual location of the oil fill/drain port in case of such issues.
Finally we have two shots of the partially roughed crankcase castings together. The next steps will be to get the outside dimensions cleaned up to size on these, cut the openings for the crankshaft, and then start on drilling a multitude of fastener holes...
My castings are still a bit rough, but improving. As I plan to paint this engine, I'm filling the rough spots in with high temperature epoxy putty, that's the brown stuff on the part. It's especially important for this one, as i had two pinholes in the thinner areas that would have prevented it from being oil tight. I suspect the cause of these to be inadequate venting of the core. As the core binder burned up the resulting gases pushed through the still liquid casting in the thinnest spots so they could escape.
I then set up to mill the part and get the main surfaces flat and parallel. The hole in the side was left by a chaplet that supported the overhanging part of the core. I was expecting it to melt into the casting (it was also aluminium) but it instead survived and left a very neat opening. That's not a problem, as I deliberately placed it at the eventual location of the oil fill/drain port in case of such issues.
Finally we have two shots of the partially roughed crankcase castings together. The next steps will be to get the outside dimensions cleaned up to size on these, cut the openings for the crankshaft, and then start on drilling a multitude of fastener holes...
A few casting observations/suggestions:
1. I have used sodium silicate mixed with sand for cores, and it works well (use the exact recommended amount of sodium silicate, and gas for 5 seconds only).
You can try baking the cores to make sure they are completely dry, and you can also bake the sand before you mix it with the binder, again to make sure you don't trap moisture in the core.
2. They recommend venting cores, and so for instance for a round core, I would use a 1/4" round wood dowel rod down the center, and when the rod is retracted, you have a hole in the core.
The hole in the core is vented out both ends into the sand mold, with vent holes extending up and out the top of the cope.
3. It sort of looks like you are overheating the aluminum melt, which is very easy with an oil burner.
Oil burners will bring 20 lbs of aluminum to pour temperature shockingly fast, such as withing 12 minutes.
4. Pour temperature should typically be around 1,350 F.
Any hotter than that and you get a lot of metal sort of soaking into the sand before it solidifies.
5. One way I have been told to judge the pour temperature, if you don't have a pyrometer, is to watch the meniscus at the crucible wall.
As soon as the meniscus goes flat, you are at perfect pouring temperature.
6. On a long thin part like that, I would probably try a knife gate, for a fast fill with low velocity.
Hope this helps.
Oil burners are great, and one never has to get a propane bottle refilled.
They will burn kerosene, diesel, waste oil, etc.
Great castings and furnace/burner !
.
1. I have used sodium silicate mixed with sand for cores, and it works well (use the exact recommended amount of sodium silicate, and gas for 5 seconds only).
You can try baking the cores to make sure they are completely dry, and you can also bake the sand before you mix it with the binder, again to make sure you don't trap moisture in the core.
2. They recommend venting cores, and so for instance for a round core, I would use a 1/4" round wood dowel rod down the center, and when the rod is retracted, you have a hole in the core.
The hole in the core is vented out both ends into the sand mold, with vent holes extending up and out the top of the cope.
3. It sort of looks like you are overheating the aluminum melt, which is very easy with an oil burner.
Oil burners will bring 20 lbs of aluminum to pour temperature shockingly fast, such as withing 12 minutes.
4. Pour temperature should typically be around 1,350 F.
Any hotter than that and you get a lot of metal sort of soaking into the sand before it solidifies.
5. One way I have been told to judge the pour temperature, if you don't have a pyrometer, is to watch the meniscus at the crucible wall.
As soon as the meniscus goes flat, you are at perfect pouring temperature.
6. On a long thin part like that, I would probably try a knife gate, for a fast fill with low velocity.
Hope this helps.
Oil burners are great, and one never has to get a propane bottle refilled.
They will burn kerosene, diesel, waste oil, etc.
Great castings and furnace/burner !
.
What does a knife gate look like? I've not heard that name before?
The bottom of my crucible was cherry red when I withdrew it from the furnace. So probably a bit too hot! The oil certainly warms things up fast once it gets going.
I've been making my cores using 2% 'bio-epoxy' as a binder. Essentially an epoxy that uses glycerol as the starting material for the resin, rather than bisphenol a. The cores are very strong (as you'd expect) and the binder thermally decomposes after the pour so they are very easy to remove from the casting, but lots of (noxious) gases are produced. For the upper block the core was supported by prints at both ends, I guess that gave it more area to get rid of excess gas, so I got away with simply the porosity of the core material plus vents in the core prints. For this one the core was 'blind' except for the chaplet, which led to problems. I think doing as you suggest with the dowel would help quite a bit.
Lets take the rectangular open-bottom piece that you cast, which I guess is the engine base.
I would ram up a drag, anchor the core in the drag, carve out a U-shaped runner around where the base of the pattern will be, and have gates enter both sides of the casting, with the gates being perhaps 3/16" tall, and 2" wide.
The sprue would enter the center of the U-shaped runner.
The pattern would be completely contained in the cope, and the mold would fill upwards.
I would use a few 1/16" vent holes from the top of the cope mold out the top of the sand.
The runners would extend an inch or so beyond the gates, and I often vent the ends of the runners up and out the top of the cope mold.
.
I would ram up a drag, anchor the core in the drag, carve out a U-shaped runner around where the base of the pattern will be, and have gates enter both sides of the casting, with the gates being perhaps 3/16" tall, and 2" wide.
The sprue would enter the center of the U-shaped runner.
The pattern would be completely contained in the cope, and the mold would fill upwards.
I would use a few 1/16" vent holes from the top of the cope mold out the top of the sand.
The runners would extend an inch or so beyond the gates, and I often vent the ends of the runners up and out the top of the cope mold.
.
So they are more or less shallow, wide gates.
I actually did initially try having the pattern entirely in the cope, but kept having misruns. Possibly this was because the casting was almost as tall as the flask, so the amount of head available at the end of the pour was very little, only 15mm or so.
I use a generous runner on each side, and generous gates on each side too, so you can fill fast with low velocity.
If you try and fill a casting with a small single gate, generally the metal flowing through a small opening will cool too fast and the fill will be too slow.
Your casting is rather tall, so you could put it in the drag, but I would still use a knife gate either side.
Waterfalling the metal into a mold cavity is not recommended, but you may have to do it.
.
If you try and fill a casting with a small single gate, generally the metal flowing through a small opening will cool too fast and the fill will be too slow.
Your casting is rather tall, so you could put it in the drag, but I would still use a knife gate either side.
Waterfalling the metal into a mold cavity is not recommended, but you may have to do it.
.
I've been milling the lower block casting. It's now close to done, just needs the bolt and pin holes that will join it to the main block. The rounded cutouts were made with a holesaw, hence the poor finish. I should have included them in the core and left as-cast i think.
Having gotten to this point, I couldn't resist doing a test assembly of the crank and rod in the lower block.
Having gotten to this point, I couldn't resist doing a test assembly of the crank and rod in the lower block.
Bad news everyone, I managed to write off my main block casting. Rather annoyed with myself right now, especially as it was almost fully machined!
The obvious move would be to cast another, but now that this has happened I wonder if I shoulde look at revising the design to account for lessons learned along the way. Also my foundry is kaput, so I need to build a new one before doing any more castings.
I can of course make other parts of the engine in the meantime. Perhaps the cylinder head.
The obvious move would be to cast another, but now that this has happened I wonder if I shoulde look at revising the design to account for lessons learned along the way. Also my foundry is kaput, so I need to build a new one before doing any more castings.
I can of course make other parts of the engine in the meantime. Perhaps the cylinder head.
peterl95124
Well-Known Member
- Joined
- Feb 22, 2020
- Messages
- 428
- Reaction score
- 258
if casting and foundry work is your thing then go for it, but otherwise its usually faster and easier to machine from bar stock
Did the piston this evening.
This all went as perfectly as could be, right up to the point where I was drilling the drain holes in the oil control ring groove and my 1mm drill snapped down inside the hole. There's no way to get it out, so I can either cast a whole new piston or use this otherwise perfect example and risk the broken drill working loose while the engine is running, in which case it would no doubt find some way to cause all kinds of havoc. I've read you can dissolve drills and taps out of aluminium parts using alum solution, has anyone tried this?
Moaning about my rotten luck aside, I'll add that the special alloy I used to cast the piston machines wonderfully, the surface finish is fantastic even when machined dry and the swarf breaks into nice little curls.
This all went as perfectly as could be, right up to the point where I was drilling the drain holes in the oil control ring groove and my 1mm drill snapped down inside the hole. There's no way to get it out, so I can either cast a whole new piston or use this otherwise perfect example and risk the broken drill working loose while the engine is running, in which case it would no doubt find some way to cause all kinds of havoc. I've read you can dissolve drills and taps out of aluminium parts using alum solution, has anyone tried this?
Moaning about my rotten luck aside, I'll add that the special alloy I used to cast the piston machines wonderfully, the surface finish is fantastic even when machined dry and the swarf breaks into nice little curls.
Roger B
Well-Known Member
Sorry to read about your setbacks 
I have used alum to disolve broken HSS drills and taps out of aluminium parts. It dosen't work with carbide tooling. You need a strong solution and some heat. It is slow and for a small deep hole you may need to agitate with some fine wire to remove air bubbles and to ensure there is fresh solution in the hole.
I have used alum to disolve broken HSS drills and taps out of aluminium parts. It dosen't work with carbide tooling. You need a strong solution and some heat. It is slow and for a small deep hole you may need to agitate with some fine wire to remove air bubbles and to ensure there is fresh solution in the hole.
ajoeiam
Well-Known Member
You've got enough work into this part.
How about buying a carbide drill - - - - either 1.0 mm or a touch smaller and then trying to peck you way through that bit f broken off drill (hopefully the chunk isn't some 6 or 8 (or more) mm).
(After you get through you should be able to complete the hole - - - I hope you can!!)
Not a cheap solution and maybe most would say that its too many dollars and my time is free - - - - imo we only have so much time left and burning up a bunch when a $10 or 15 solution would reduce that time demand - - - - I'm spending the $$$.
HTH
Scott_M
Well-Known Member
Hi Nerd
Bummer.
Has the drill broken through? Is it broken off below the bottom of the ring groove?
The reason I am asking is maybe you can leave it in there and trap it. If it has not broken through all the way you won't have to worry about that side, If the drill is proud of the hole maybe grind it down flush with a little Dremel abrasive disc and then either a punch mark around the hole or fill it with epoxy. You should be able to trap it and save the part.
Best of luck with it !
Scott
Bummer.
Has the drill broken through? Is it broken off below the bottom of the ring groove?
The reason I am asking is maybe you can leave it in there and trap it. If it has not broken through all the way you won't have to worry about that side, If the drill is proud of the hole maybe grind it down flush with a little Dremel abrasive disc and then either a punch mark around the hole or fill it with epoxy. You should be able to trap it and save the part.
Best of luck with it !
Scott
peterl95124
Well-Known Member
- Joined
- Feb 22, 2020
- Messages
- 428
- Reaction score
- 258
I've never succeeded in drilling out a small drill or a small tap, even with carbide, I have succeeded in dissolving a tap broken in aluminum with nitric acid, took several days but its a hobby so no rush, I must add though that nitric acid will definitely anodize the aluminum and change its external appearance, for a piston that probably improves its surface coefficient of friction but for the part I was working on I wanted that original machined aluminum appearance so made a dam out of wax to keep the acid from getting all over the part.
If you can get the drill out, you could tap a hole and thread in an aluminum plug, and then re-drill the hole. But I think re-making the piston is more your style. Do what makes you feel comfortable.
Did you find a high-silicon alloy to cast with? Or maybe some scrap automotive pistons to melt down?
I am curious. You used a cast iron liner, too, correct? How did you find a cast iron tube, or whatever you used. You are quite resourceful!
I am curious. You used a cast iron liner, too, correct? How did you find a cast iron tube, or whatever you used. You are quite resourceful!
NapierDeltic
Well-Known Member
I subscribe to Scott_M's post and solution. I have bad experiences with mechanical removal of broken drills.
Good luck!
Good luck!
I tried the alum trick and it seemed to be attacking the aluminium as much as the iron- there were lots of little hydrogen bubbles coming off, and it noticeably dulled the surface finish. So I put a stop to that. I can only speculate as to why, perhaps this alloy (grade AA337, for the curious) is not corrosion resistant enough to avoid being attacked by the alum solution.
The drill was broken off below the bottom of the ring groove, so I've trapped it by peening the hole over with a punch.
I doubt there will be any issues, in any case running a model engine hard enough for an extra 1mm blind hole to cause a piston failure is probably worth bragging rights anyway.
The drill was broken off below the bottom of the ring groove, so I've trapped it by peening the hole over with a punch.
I doubt there will be any issues, in any case running a model engine hard enough for an extra 1mm blind hole to cause a piston failure is probably worth bragging rights anyway.
