im stressed with patterns

[johnthomp]

ive been trying to make a reuseable pattern for a 5" flywheel with curled spokes for 8 months now and i cant do it if i manage to make the two halfs to match then seperate them when i try packing them in the sand the spokes either snap or buckle under the preassure the last one i made in pieces out of maple wood thinking it would be strong enough but it also buckled im loseing heart with this and there must be a certain way and matereal you all use for such delecate patterns i cant even find any videos on the interweb showing how to get away with this is there a thread on here for this or can anyone give me a few hints as to how the hell its done correctly
i hope you all can help because the advice you all gave me about the bentonite clay in kitty litter was absolutely spot on and its a shame i cant use it on the most needed thing at the moment wich is a flywheel HEEELLLPP !!!

 

[steamer]

John,

I would suggest using a match plate. That will support the pattern while your ramming...Its little more than a firm heavy piece of plywood with the pattern glued to it, on half on one side and one half on the other....here are some photos , I would have had the same problem with my launch engine columns otherwise.

Dave

 

[johnthomp]

i never thought of that :noidea: ive been trying to make a wooden flywheel in 2 halves set them with locking pins then pack them in a pair of flasks this is when they break im gonna try this method over the weekend to see how i get on :bow:

 

[Cedge]

Not all curved spoke flywheels are castings. A number have been made from bar stock with great success.

Steve

 

[tel]

OK. this is not a flywheel, nor does it have curved spokes, but it will give you an idea. Make your pattern in two pieces, install a couple of locating pins to hold them in the correct orientation, then drill holes in your match plate to take longer pins and pop your pattern halves on them. Too easy.

 

[JohnLanark]

A friend who is retired patternmaker once told me that his way to make curved spoke wheels is to make just one wood spoke pattern with double shrinkage allowance, and cast as many as are needed for the wheel. These metal spokes are then fixed to the rim pattern. That way they are all identical and strong. John

 

[steamer]

OK. this is not a flywheel, nor does it have curved spokes, but it will give you an idea. Make your pattern in two pieces, install a couple of locating pins to hold them in the correct orientation, then drill holes in your match plate to take longer pins and pop your pattern halves on them. Too easy.

That is exactly how I did mine....worked great, and I can tell you the foundry was not gentle with them either and they held up beautifully.

Glad it helped...

Dave

 

[ART]

I made a curved spoke flywheel pattern last winter that was 7" dia. It was split through the center and had two short pins in one half to locate the halves together. I placed the half without the pins face up on a board set half of the flask on the board and rammed in the sand. I then place another board on top of the flask and turned the whole thing over with the flask/sand/and half of the pattern sandwiched together. I removed the first board exposing the pattern along the parting line lightly brushed off the sand when I applied the parting dust, set the second half of the pattern in place on the first half, set the second half of the flask in place, and rammed it up with sand. I split the flasks removed the two halves of the pattern cut the runners and sprue and reassemble the flasks. I cast the flywheel with zinc. It came out great. ART

 

[johnthomp]

art thats the method ive been trying due to haveing much sucess with a few experimental engine bases i made my trouble is when i rammed the seacond side up with sand i must have rammed my wooden block through the centre of the wheel and broke the spokes sending me back to square 1 im currently in the process of makeing a parting set board like the ones i have been showed to see if i can get them right
just one question though is there anything better that talcum powder for a pattern release agent it seems to get stuck in the corners of the mold sand or is that just me useing too much
but i think i have got it right with useing fibreglass resin to smoothe out the surface of the pattern by dipping my pattern in it then putting the part in one of those vaccume storage bags then sucking the air out it dont half put a mirror finnish on the part and leaves no sanding later just knife the dribbles off the edges
john

 

[ART]

John, I have used molding boards for several of my more complicated patterns, but just the split pattern for the flywheel. From your last post it sounds like you may not have rammed the first flask hard enough to support the second half when it was flipped over. I ram the first half somewhat solid because that half will be on the bottom of the mold, and the gases will be vented through the top half. I ram the second half a little less dense to vent these gases, but not so loose as to fall out when the pattern is removed. I use commercial parting dust but talcum powder should work. I put mine in an old sock and just dust it over the pattern. If some falls into the corners I just leave it there. I just use a can of spray paint to put the final finish on my patterns. If there are no undercuts and adequate fillets then the pattern should be able to be removed easily with a good finish. Art

 

[johnthomp]

sounds like i been doing it the wrong way to begin with this is the first time i have attempted a 2 part mold i have only ever done the odd floor cast before now in an old biscuit tin worked pretty well though
cheers for the advice and spray paint sure sounds a lot easier than resin coating im still at it whittleing a new pattern up at the moment but ill let you all know how i get on shortly
john

 

[Artie]

Hi John, from what I can glean here it sounds like you are trying to ram up with too much force. As ART has said you only need to get the sand in to fill the voids with a small amount on compression so it stays in shape. The sand needs to be a little loose to allow the (massively) expanding gasses to vent.

I also push a bicycle spoke through in various spots to aid this.

Incidentally excess clay can inhibit the venting process as well, the result is you end up with pockets in corners etc where the gas couldnt get away fast enough as the metal solidifys.

There is another way, if you scroll down to reply 57 from Dave in this thread he has an idea that may also be useful, this an Odd Board or Ramming Board. Its pretty easy to see how it works and the pattern is a solid unit rather than the split style.

http://www.homemodelenginemachinist.com/index.php?topic=7380.45

I use talc for parting powder and it works well, just get a very soft bristle paint brush and after you blow off the excess (breath) give it a couple of swipes and blow again.

Good luck, it can take a few goes before it comes out right (it will come put right mate).

Rob T ;D

 

[Lakc]

One of the things I have learned about pattern making, is the real professionals are not trying to make patterns from the lumber section of Home Depot (or insert name of local big box hardware store here). Its easy to sand too far or get too much ramming deflection in softwoods or use too much dynamite working from old pallet hardwoods. :
Beautifully finished patterns with no filler and excellent dimensional stability are the reasons the patternmakers get the big dollars around here, where they are used as much for sheet metal form checking as well as foundry work.
Here is a local (to me) place that sells professional patternmaking lumber.
http://www.mccauseylumber.com/mptb.html
One guess at the prices of this stuff, are somewhere between lottery winner and major corporate customers.
I have since learned not to stress out about my pattern quality. Doing a single spoke in hard metal and duplicating it, sounds like the best way for a home shop to go about your problem. Since we dont likely have all the high dollar tooling and materials, we have to turn to those ingenious workarounds.

 

[Bernd]

Another place to get wood for pattern making is a local wood working store or look for them on line. Rockler comes to mind. See if there are any woodworking clubs in the area. They can help with locating hard woods for pattern making.

Bernd

 

[kf2qd]

I used to work for a company that built pottery equipment. Had a bunch of old patterns. The old ones were all made from mahogany. They were works of art...

 

[johnthomp]

i think now i finaly have a pattern that will work it works ok in my daughters sandpit so im gonna see if the weather and family life will allow me to melt some scrap over this weekend
i would put pics of the furnace in use but im not sure weather or not anyone would see it as a safe machine as its wood fired and i have no doubt someone would poke me with the safety stick stickpoke so ill just send in the before and after shots
see you all soon
john

 

[dsquire]

John

For your daughters sake if not for your own please tel us what you are up to as far as casting metal. I personally am not able to give any good advice on what to do or not to do. There are many on the forum and some that are very near to where you live that will be able to tell you if what you plan is good or bad. None of us hear want to hear that you have been injured or burnt in any way. We certainly don't want you daughter not to have daddy all in one piece.

Expecting to hear from you shortly John.

Cheers

Don

 

[johnthomp]

relax fellas i use an old steel tub with a grate in the bottom fed air via an old hairdryer that i made work on 12 volts by dismantleing it just saw a rating on the motor saying 12v dc i run this on a car battery via 3 feet of tube bent and buried in the hard clay ground at the top of the father in laws garden out of the way of any children and distractions
the tub has my crucible pot sat in the middle with the scrap alu already loaded and is just an old stainless steel kitchen pot from my late grandmothers kitchen (she used to make some cracking puddings in that ) the top of the pot is drilled right through at 12 mm to accept a 4 foot length of steel rod with a hook roughly 10" from one end so as the bar slides through the holes and contacts with the hook it locks the pot to the bar for pouring leaveing me a good 3 feet at the other end to keep me out of the way and with good controll of the hot pot
when me metal is hot the rod is used as described and the pot when finished with is placed in the centre of an old brake drum from a series 2 landrover as its heavy and the pot fits in the hole in the middle enableing me to hold it still while i remove the handle (so i dont trip over it )
i then if theres no more casting to do turn off the blower and put the wood out with wet sand and leave it to cool then later remove the sand and clean the furnace out ready for storage
i prefer to use wood for my fuel as its free for us joiners to take a couple of bags of offcuts home and i must stress that i only ever cast in aluminium coz its what im used to i send all my brass casting projects to a local foundry that specialises in bronze and brass they also do it cheap if i give them a bag full of brass door furnature (especialy something we know as carlisle cast brass ) as they have remarked that it has a verry nice flow to it when pouring and hardly any gas build up
regards john

 

[Artie]

Any updates? Did you get a result? Keen to hear more......

 

[ozzie46]

Artie, I don't believe johnthomp is a member now.

Ron