Repairs to a Bandsaw

[Meldonmech]

Hi Guys
             When using my Bandsaw recently I heard a horrible sound from beneath the work table, and immediately stopped the machine. On investigation I discovered the lower blade  guide die casting had broken. The design was flimsy in the area where most of the downward blade forces were acting. I glued a piece of wood to the area that  needed thickening up, then glued the casting back together.

[Meldonmech]

 
    For some time now I have wanted to attempt lost wax casting, and thought this would be the ideal opportunity. I made a wooden pattern, and added a runner/riser.
 I purchased some rubber moulding medium, and made an adjustable mould box from four pieces of " L" shaped wood I had nailed and glued together. These were held together with finger clamps. The pattern was placed in the mould box, the rubber was melted and carefully poured into the mould box. When set the mould box was removed.

[Meldonmech]

 The rubber mould was then carefully cut open and the pattern removed. Casting wax was then slowly melted, while the mould was turned over to expose the pouring hole , then taped around the outsides to keep the mould closed. The mould box was replaced around the rubber mould to give added support. The melted wax was then poured into the mould and allowed to cool.

[Meldonmech]

 
The wax replicated pattern was removed from the mould when cooled and smoothed off using a hot knife. The wooden mould box was reassembled, and the wax pattern placed in the box.  Casting plaster was mixed to a thick cream and was the poured to fill the mould and allowed to cure.

                                                       Cheers  David

[Meldonmech]

 When the plaster had set, the mould was turned upside down and placed in the oven over a small bowl. The mould was heated until all the wax was removed. Then the mould was cooked at 220 c. for an hour to remove any moisture left in the mould.
       Aluminium was melted in the furnace and poured into the plaster mould until filled. A large bubble of aluminium rose from the mould, and then burst.  I realized I had a problem, and suspected a steam bubble.
       On cooling the mould was broken open and the casting removed. Luckily I had left a generous machining allowance on the pattern and thought I might be able to use the casting.

                                     Cheers  David

[awemawson]

David,

Sorry to see the bubble. When I was experimenting with lost wax I used to bake my investments for much longer than an hour.  First I used a steam wall paper stripper to melt as much wax out as possible, then I used a pottery kiln at maybe 150 C for an hour or so for any remnants to drip onto a baking tray, then I took the temperature up to over 300 C for several hours

[Meldonmech]

    Andrew
                 Next time I have a plaster mould to dry out, I think I will leave it on one side until I am melting alumiuium, then pop it in the furnace whilst the furnace cools down. May have to warm it up in the oven first to avoid any shock.

                                                                           Cheers David

[Meldonmech]

 
    The casting machined up quite nicely, and as I gradually worked through each operation, began realize that the casting would be usable. The band saw blade guides were originally held in square holes.  I milled square slots then covered them with a bent angle piece made from aluminium sheet and held onto the casting with screws. There is a 6mm ball race which takes the thrust of the blade, which cannot be seen on the pics. 
            The device was assembled and re fixed to the saw. Trial saw cuts were made on the saw, and the saw is cutting true again.

                                                   Cheers  David

[awemawson]

  Glad it turned out ok in the end