[epineh]

So close but so far...

Pretty much good news bad news, the good news is that the surface finish was good, but unfortunately the metal didn't flow completely into the foam.

I am happy with the slotted holes as I was worried they would fail due to how close they were to the sides, but they were mostly perfect.

I think I need to change how the metal comes in, probably more in the centre of the pattern, so it can get in as hot as possible to both ends at the same time rather than fill from one end through to the other.

Got plenty of foam, back to the drawing board, though to be honest as it is the part would most likely hold the servo, just doesn't look the best.

Russell.

[CROSSHATCH]

Great stuff man. Really cool work

[rotonone]

So close but so far...

Pretty much good news bad news, the good news is that the surface finish was good, but unfortunately the metal didn't flow completely into the foam.

I am happy with the slotted holes as I was worried they would fail due to how close they were to the sides, but they were mostly perfect.

I think I need to change how the metal comes in, probably more in the centre of the pattern, so it can get in as hot as possible to both ends at the same time rather than fill from one end through to the other.

Got plenty of foam, back to the drawing board, though to be honest as it is the part would most likely hold the servo, just doesn't look the best.

Russell.

hi there Russell came across this thread after looking into your work with the linistepper controller you made great work there I am really ken to find out how they have performed since and weather you used a PIC or connected straight from the PC.

just wondering what sort of casting ceramic you are coating your foam in to maintain the shape and what type of backing sand you are using as well? also I noticed your casting does not allow for the "dross" in the molten aluminium I would suggest you change your risers so that the metal enters into the base of the pattern which will help in ensuring you casting does not cool too fast. Also if you can incorporate a filter to clean up the flow of the metal and reduce turbulence this will result in a better quality casting. you also need to be very careful with the fumes that come out toe foam as well I would suggest using some sort of fume extraction which can be directed away from persons.



Cheers Bill

[epineh]

Hi Bill, yup you are right I need to change things a little for that to work, I thought since it was a nice thick casting that I might get away with it...almost, lol.

For the coating I am using Gyprock TopCote, watered down enough to paint consistency and brushed on, I think about 4 coats did the trick, very happy with the result.

Sand is dry brickies loam, and I always cast outside for the fumes and general safety. I will take your advice on board for the next pour.

The linisteppers were a fun project, one that I hope to re-visit one day, the high step modes were something to watch, smooth and silent. I was running them via PC, I think I was using TurboCNC at the time.

Cheers.

Russell.

[rotonone]

hi Russell

one of the problems with using topcoat is that that it is used as a finish coating and as such gives a smother finish for plastering. Unfortunately fort eh process that you are using if for it will not allow from the gas to escape from both the casting process and from the burning foam I would recommend you use base coat a the very least and back it up with washed river sand and don't pack it as this will also allow for the gas to escape. one other option is to put more risers on the pattern but this will mean you will have to have more metal to cast it the pot. one other thing you might want to look into, if you haven't already, is degasing tablets to remove the hydrogen from the casting which will help remove the porosity.

here is a good guide to get you started if you haven't come across it already Lost Foam Casting

I'm certainly keen o see how your parts finally come out good luck and if there's anything I can help you with let me know

cheers Bill

[lukewarm]

Casting!

Love it. Casted my gantry risers and Z plate myself. I learned a few things doing it. The first thing I notice with your servo bracket is you only have one inlet and no outlets. Add more! Add another large inlet on the thin areas otherwise you won't get proper fills and you'll have shrinkage issues.

I tried plaster topcoats but I found the best way to get a nice surface finish was to cover the foam in painters masking tape! It gave great finishes and you didn't have to wait for the plaster to dry and worry about it not being perfectly dry. Please try using masking tape! I've tried everything and masking tape worked awesome! I haven't read the rest of your thread so I'm only assuming you are getting your aluminum hot enough to flow properly. If it's too cool it won't flow into the mold properly.


If you have any questions please feel free to shoot them my way. I've failed on so many castings until I found a technique that worked well that I'd like to pass the info on if I can!

[epineh]

Well I have never heard of using masking tape, lol. Sounds like I need to give it a go.

Does the tape "dissolve" like the foam or stay more or less intact ?

I can see it being really good in that you could use standard packaging styrofoam and not get the bead pattern on the finished casting surface, also it is practically free as I have to buy XPS here and it is a bit of a pain to get in.

Cheers.

Russell.

[Jere33my]

I've failed on so many castings until I found a technique that worked well that I'd like to pass the info on if I can!

[lukewarm]

It sticks around as black soot that washes off.

Not sure if it works well with EPS but I don't see why not. I always used the pink foam insulation I buy at the hardware store here.


Just remember thin areas need a reservoir of molten aluminum attached to prevent shrinkage issues and those hot foam gasses need to go somewhere! Give them escape routes on the opposite side of the mold and once you see aluminum coming out of those then your casting should be good!

Do you use a head pressure device? They are fairly critical!

[epineh]

Do you use a head pressure device? They are fairly critical!

Well I figured I had a pretty high in feed path, turns out not enough...(chair)

Any Hoo, got a bit bored this week due to lack of funds to buy stuff for this build so I thought I would play around with the limit/homing switches.

I am going to use the electronic ones as per the RomanLini's thread here on the Zone. I had some 15mm perspex lying around and instead of machining it out I got lazy and drilled a few holes in strategic positions and then epoxied the hall switch and an LED inside, pic should make sense of it all...I don't have the correct magnets yet so I cannot make the base piece.

Cheers.

Russell.

[epineh]

Did a little more today, I am going to use some photocopier drawers for the electronics and also for storage of bits, tools etc.

I won't make much of a cabinet maker as these four took me all day to install, although I did mount some of the electronics as well so it is getting there.

Cheers.

Russell.

[epineh]

Cabled and powered up the power supplies and controller electronics, all ready for testing back to the PC.

If anybody is wondering at this stage I am going to be running EMC, well actually it is called LinuxCNC these days, on the latest 12.04 desktop version of Linux, utilizing the ArisRobo hardware and a 7i43 MESA card. I am having a bit of trouble getting the software to load but that will be sorted this week hopefully.

The dodgy looking switch you can see in the bottom left side of the controller section is just a temporary axis/spindle motor enable until I get the I/O board up and running and tie it into the PC.

Cheers.

Russell.

[epineh]

Little bit more, Chich has kindly dialled in the X axis linear rails and ballscrew assembly, all that is required now is to make a packer to bolt the ballnut mount to the X/Y plate, then the X axis is mechanically finished !!!

I made a motor mount plate and bolted that onto the end of the linear rails, this also acts as the hard stop. Next is to make some motor mount spacers and the axis will be complete.

Once that is done I intend to make all the machine covers up to the X/Y plate, then the whole thing should start looking like a real machine.

[epineh]

Over the weekend I assembled the first servo drive, this will power the Z axis which is 24V, the brake is the same voltage so that is handy. I have built the old faithful Elm Chan drive and I have to say I was reminded of how nice it works, had the motor holding position in about five minutes of total power up.

As always pics or it didn't happen !!!

Russell.

[epineh]

I feel the previous pic was too neat, so here is another one zoomed out a bit, with all the usual testing clutter, haha.

I built a temporary power supply with multiple voltages for initial testing of the drives as you can see at the top of the picture, test servo is bottom left, the one to the right of the drive is the actual Z axis servo, after playing with the test one I plugged the brake wiring into the power supply to test it, with power on the brake releases as it should, I will tie this to the machine enable signal, drives go on, Z brake goes off.

I can't connect the servo to the drive just yet as it has no encoder, another thing on the "to do" list.

[chich2]

Nice work Russ!!!!!! Must say I do like the encoder inputs : D

[epineh]

Haha don't judge, I did say it was a test rig, so anything goes as far as I'm concerned !

[chich2]

Is that the brake output on the top left of the servo drive? What are those wires?

Sent from my MB525 using Tapatalk 2

[epineh]

Nup, that is the serial port, brake will simply be tied to the machine enable, no connection to the drive at all.

[epineh]

Quick check of the Z servo reveals my encoder will simply screw onto the end, I am going to use sikaflex to stick the X and Y encoders on, I have a friend that does that all the time without issue.

Might have to give the stub a clean up, been sitting around too long by the looks of all that rust !