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Richard's Pattern Making Blog


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Day 14 - Monday, 10th June 2013:

Back on the woodwork lathe, my father is asked to turn up the core spindle. This will not form part of the pattern but is a component needed to make the pattern itself.

It is machined to a length which is longer than the casting as the extreme ends will locate in 'core prints'. These can be seen at the ends of the grey pattern and locate the sand core in its suspended position. What is effectively being built here is a moulding box so I can then replicate the wood in casting sand. It is this sand core which produces the hollow in the casting.




Here is is. It is made on oak although for no particular reason, just a surplus off-cut. This will arrive back here tomorrow and then I can start building a moulding box or 'core box' around it although in two halves.











Day 15 - Tuesday, 11th June 2013:

Next, I need to make both halves of the moulding box, or 'core box'. The oak spindle pattern will sit half and half in each box and will have pattern maker's resin poured around.









Note that the right hand box has small timber fillets inserted around the neck. These are also placed under the spindle although they do not touch it. There are two reasons for this, firstly to prevent a large build up of resin at any one point as excess depth can cause the it to contract during curing. Secondly, the resin is rather expensive so I want to use the minimum required. Both halves will be built up with fillets in the same way before I pour the resin in.

Both boxes have temporary end caps. This is purely to prevent the resin from pouring out the end. These will not be on the finished core box in order to allow sand to be rammed up from both ends of the mould.





Day 16 - Wednesday, 12th June 2013:

The spindle pattern is suspended in the first box using panel pins at either end of it's axis.










The end plates to the box and the spindle are coated with release agent so the resin will not adhere to itself. If it did then I would have a major problem!









Pattern maker's casting resin is poured in which flows underneath the spindle and fills up to the top of the box.









Half an hour later, the resin is well and truely cured so I can remove the end plates. I can then also remove the spindle and sand off the excess resin with the disc sander so I have a flat surface for the other half of the moulding box to sit on top.








One half done. Tomorrow, I will pack up the second box with fillets of timber, just like I did previously and then match the two halves up for the next process













Day 17 - Thursday, 13th June 2013:

The top box is prepared in the same way as the first.










One box is placed on top of the other. Two holes are drilled all the way through the top box and an 3/8th inch into the bottom box. Steel dowel rods are inserted all the way through and diagonally to each other. This is so that the two halves can always be locked in position again after the resin moulds are separated.







A resin feed hole and an air hole are also drilled in the top (right) box. End caps are also temporarily placed on each box.









The oak spindle is coated with release agent, along with the resin face and both mating faces of the box halves.

Tomorrow I will pour in the resin and then break open the mould.










Day 18 - Friday, 14th June 2013:

The two halves are then held tightly together using four long wood screws otherwise the resin goes everywhere!









The resin is poured in until it appears out of the other hole.










The resin is thin and so will find the smallest of holes to escape. Therefore, for the first couple of minutes it may be necessary to occasionally top up until the resin starts to cure and stops leaking.

This pattern will be fully finished tomorrow morning. I have spoken with the foundry this morning and if I can get the pattern to them on Monday next week then they are going to try to have it cast by the Wednesday. There will hopefully also be a full set of photographs showing the whole foundry process in stages so do stay tuned in folks.







Day 19 - Sunday, 16th June 2013:

Here is the core box with the end plates removed and with the pattern still in the top half. The spindle pattern will be extracted and is no longer needed.









And here is the finished pattern, well hopefully! On Wednesday I should have a sample casting and then I can carefully examine the finish to establish if I need to make any final adjustments to the pattern. My main reservation at this stage is the recessed joint line on the top right corner of the grey pattern as when this is all filled with sand, there is potential for the sand mould to break at this point. If this happens then I will simply widen the recess to strengthen the sand mould.

Let's see what Wednesday delivers......






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