Puppet on a String---Pattern Lift Method

Here are a couple pics of a pattern lift method I tried out today.

Deepish patterns are tricky to lift, I think, as they are hard to pull straight up out of the mold. I have used a hydraulic system that works quite well for very large deep patterns like those 48" in length and also 36" inches. But I have been hand pulling smaller ones with pretty good results. But I occasionally bruise the edge of the mold due to clumsiness. Part of the "clumsiness" comes from the fact that the draft we so carefully build into the patterns causes them to naturally wedge back into the mold as we attempt to tap upward on our draw spikes in an effort to free the pattern. Indeed, on the end of the pattern I tap on the pattern may ultimately tap upward a quarter of an inch on that end. But having only two hands, I have to let go of that end and then tap the other. Well, the first end just sinks back into the mold almost all the way. Switch ends and the same thing repeats. That is frustrating.

So, I thought that it might be useful to have a simpler system for smaller molds that would support the non-tapped end while I worked on the other end and that would provide a straight line of lift.

What I came up with (and my apologies if this is actually an idea that dates to, say, 1912) is to use a bar suspended over the mold and carrying two pulleys. The pulleys carry one string each. Each string connects to a draw spike on one end and to a stick---the puppet control--- on the other. Since one string is on one end of the stick and the other string is on the opposite end of the stick, it is possible to vary and control the pull delivered to each string. So, after tapping one end loose, it is possible to prevent that end from falling back while the other end is tapped. Once both ends are pretty well tapped loose, pulling evenly on the stick draws the pattern smoothly from the mold.

What I made is pretty crude. I simply hook a support bar from the back of my bench and then place a round tube (recycled mop handle!) on the supports and secure the bar with rubber bands to prevent rolling out of position. (I will be improving this method of securing the bar with a simple but a bit more secure attachment method.) It is important to make sure the pulleys are positioned to provide a truly vertical clean lift to the pattern. This is not hard to determine as the draw spikes suspended by their strings act a plum bobs prior to screwing them into the pattern.

The system worked pretty slick for me this afternoon. I took a couple of pics but no video as I was by myself and time was limited. I'll try for video another time. Since the pattern is similar in color to my sand, you will have to look closely to see the outline of the patterns. I am attached to one of two patterns in this mold in the photo below.



Here is a plywood and 2X2 support for the round bar. I wanted it to be very quick to attach and remove as I did not want it to be in my way when doing tasks other than the actual drawing of the pattern. This fits just slightly snug on the back of the bench. So it is not wiggly and is very quick and easy to set in place and to remove.

FWIW.

Denis

 

I am learning to use this system. The next time I used one hand to steady the pattern to prevent swing. Both pulls were clean

Denis

 

simple and effective!

 

A possible improvement: put sharp v-grooves in the rings on the pipe and add set screws to them. After tapping to break adhesion, do the lift by applying tension with the stick (seating the strings in their grooves) and rotating the pipe for a very controlled, parallel lift.

 

I think what you are suggesting is reasonable.

But, a PARALLEL initial lift was not wanted. The whole idea was to support the tapping loose of one pattern end while the other end remained lower in the sand and then to be able to maintain the lift just achieved and go to the second end and raise it some. This process repeats until the the pattern is free of the grip of the sand. Then the stick is pulled down and a smooth draw is achieved. Once free, it is not hard at all to get both ends to come up level just by minding the pressure applied to the stick.

If you are suggesting doing the freeing tapping and lifts as I am and then tightening setscrews in the pulleys to the bar, that would help keep level, but in practice, seems not necessary and would require fiddling with set screws while maintaining string tensions to prevent the pattern falling back into the mold.

This works well and is a huge improvement in my shop over freehand pulling patterns that are relatively deep compared to their width. Flatter patterns like gear blanks, plaques and so on are simple to freehand lift and I would never use my puppet method on them.

Denis



Denis