Today I started a new pattern to make a metrology parallel/level

I did get the pattern split without incident. I was very careful and did use a newly-sharpened blade and a pressure-guide to keep the cut straight. I was a bit worried about the two plastic bolsters wondering if one of them might crack or be dislodged. But everything went smoothly.

Then I started gluing them onto the 3/4" plywood matchplate. I used thin cyano to attach the two pieces and was super careful to not get one side upside down with respect to the other side. Making such a senseless error would have been so easy for me. I checked and rechecked before committing glue. I did drill the registration holes and thought later that one fairly fail-safe method of ensuring I would not make a reversal would have been to bore just one centered and one well off center. As it was both were dead center. So, flipping the wrong way would have been easy.

One new technique for me today was making micro-fillets using thin cyano. Where the pattern meets the plate I wanted to provide a tiny fillet. Something on the order of .016 inches would have been fine. So, after getting the two halves glued down correctly, I spread a thin bead of liquid cyano glue along the join line. Surface tension pulled it into a nice radius. I knew that spraying the wet fillet with cyano activator would cause it to foam up into an ugly hard mess. But I was impatient to have it set up and open thick wet cyano sets pretty slowly. So, I stood back about three feet and just gave the wet cyano a couple of very brief puffs of activator. It worked! After about 30 secs the cyano had set but it did not foam. Yes!

Here are some pics. Eventually I intend to pour two castings per flask. I'll make a copy pattern using Repro. For now I am just mounting one front and back pattern half to the plate figuring there may be some bugs to work out. That is why the pattern is offset from the midline. I Bondo'd the registration holes. The surface of the matchplate has a couple of casual coats of shellac. The plate itself will not be highly finished as experience has shown the flat surface of the plate need not be particularly refined to pull cleanly. Different story for the vertical parts of the pattern, of course.


The cyano micro fillet


I hope to finish setting up the plate tomorrow (I'll hand cut the runner, splash basin and gates for the shake-down casting sessions. Once I know what works, I'll convert to permanently adding those features to the plate.)

Denis

 

Looks great Denis!

 

Continuing the saga of bringing a new parallel to life: I got the pattern painted using lacquer, waxed it, coated it with graphite and talc and gave it a whirl packing it with green sand. Overall, it worked out really well. There was one tiny pock mark in one corner of the drag half of the pattern. I had looked the pattern over pretty well I thought. But the sand "found" the pockmark causing a repeating small area of cracking of the sand. The area was small enough and not dislodged. So, I was able to very gingerly tamp it back into place. I think it will hold up to the flow of molten metal. I'm not certain it will. But I think it is likely to be OK. Other than that problem the pattern pulled very nicely once I figured out how to lift the matchplate without bruising areas of the mold. (Each new pattern requires some time to learn its peculiarities. It would be very rare to just pack a new mold and have it pull just right the first time and every time thereafter.)


Here are a couple pics:
The pockmark was in the cope side of the pattern right in a corner.


Closer pic---the actual defect is in the center of the dotted circle.


The drag side of the mold. Later I cut a splash basin, runner and gate into the sand.



The cope side.


I will place a ceramic filter in the srue base. You can just see the sprue mold deforming the sand to the left and slightly below the mold cavity below. It will be above the splash basin in the assembled mold.

I'll fix that pock mark with a tiny bit of Bondo.

20-second video survey of the match plate pattern:
https://youtube.com/shorts/8u6fCejwARE


Denis

 

Teaser: to late to do a reasonable write-up. But....

Summary: No defects!

Denis

 

Very nice. Is that the Repro material? A couple more then on to the production match plates?

 

No, that is iron.

I intend to work on making another pattern or two using Repro quite soon.

Denis

 

Sorry to be slow giving more of an update on the new casting. Been kinda busy.
I did use the matchplate mold and had quite good luck with it. I did get some fin formation likely due to slightly wonky flasks that really are for a different split pattern. A little twist is forgiven when using a split pattern as the twist might slightly affect the part line. But the cope fits snugly on the drag regardless. Not so with a matchplate and I knew that going into it and I knew the selected flask was large enough for the plate even if it was twisted a bit. Before casting again I will make a dedicated wood cope and drag and plane them so they meet on a flat plane. I'll use 2X4" lumber with shallow lap joints and long GRK wood screws.

This is the drag side.


This is the cope side


Side view. you can also see the tumblehome of the pouring basin sides here.


You may notice the sprue is quite massive leading down to a 2" square area. In that square is a ceramic filter. The sprue is so large so as to give good access to the full (well, almost full) face of the filter as the filter would restrict flow if only a 1/2" area was accessible. Never tried that small sprue on a filter, so don't know that for a fact.

You might also judge my gate to be needlessly large. And you might be right. But, in my foundry, it seems that large gates help me avoid vacuum defects at the gate. Anyway this mold filled very quickly. I'd say it took maybe 5 seconds or so.

I used no vents and no risers. I poured at about 2525F

The fins broke off easily and I used my belt grinder to grind the seams down a bit. Then I used a die grinder and carbide bits to smooth off the inside seams. All that took less than ten minutes.

I've done some work on the pattern to remove the pockmark and smooth some fillets where the pattern meets the plate.

The next learning curve will be making a POP mold into which I can pour Repro to reproduce my wood pattern. I'll set up a plate with two patterns on it so I can cast two parallels at a time.

Denis

PS Thanks, guys, for the likes and for bearing with me on this!

 

Having satisfied myself that the pattern could be cast successfully, I am now ready to start down the path of making Repro duplicates of my wood pattern. I want to set up two sets on a match plate so I can cast two parts per mold.

I was pretty sure I'd try POP as my mold making material in which I would cast the Repro. And I posted the link to a seemingly good monograph on the subject and watched a good number of vids by various fairly accomplished artists. But a few very experienced casters expressed their reservations about POP. And I was nervous about pouring Repro One straight onto my wood pattern to make a negative mold as I was worried it would stick to the mold and be difficult and potentially damaging to remove.

So, I chckened out and pulled out a Smooth-on Vytaflex 60 two-part urethane rubber kit and made a negative mold with it. The kit has been around for a couple years, but was unopened and seemed in good condition. So I mixed up abou 2/3 of a pint and poured it into a form I had prepared.

The basic picture frame for the mold. I did put a bead of silicone rubber between it and the match plate to prevent the urethane rubber leaking out. I am not sure that was needed.


To conserve rubber I made spacer blocks to attach to the under surface of the lid. I had to be careful to allow clearance for the two bolsters in the center bay. It would have been easy to put them in upside down.


Spacer blocks screwed onto the lid.


I drilled a lot of holes with a Forstner bit so I could monitor the pour. (I guess you could call them risers ;-)

Then it was time ot mix, mix, mix and pour the rubber. It poured nicely. I'll have to wait until tomorrow to demold, though.


Even if this mold is not great for some reason, it should not damage the pattern. However, the way it all went together, I have high hopes for a nice mold. Thank you ESC and Kelly for probably saving me some problems using POP or Repro.

Denis

 

No, I did not plan on casting the Repro working patterns directly onto the match plate. Maybe I should consider it. I had planned to just open cast the Repro and then true up the open face portion and then glue it onto the match plate. I guess casting it onto the plate might save some fairing at the junction of the pattern and the plate?

It would not be that hard if I wanted to do so, to drill diagonally into the Side B mold cavity area after attaching the Side A portion of the pattern. Both injection and vent holes could be made. Using a pressure pot, attaching the needed line, cleaning the pot and lines, etc would involve a fair bit more work, though. Are the major advantages of injection molding I am missing?

It looks like the cost of tin-catalyzed silicone is similar to the two-part urethane rubber I am using. Does the silicone offer special advantages over the urethane? The urethane does not require degassing. Evidently, the silicone does need to be degassed. Silicone rubber evidently releases more easily from a pattern piece.

Denis

 

I think I can just use a nice square plate and measure within a 64th from edges to get accurate enough placement of cope and drag. If I were repeatedly positioning, I'd use pins.

Happily, I have previously used this urethane rubber with the lacquer finish I used this time. But good point to remember

I was careful to pour slowly and part of the reason for all the holes in the backing plate was that they allowed me to see how the pour was progressing and see what bubbles might be included.

Denis

 

I did pull the urethane mold off the wooden pattern this morning. And PULL it was. Even though I had a couple of years ago used the identical Urethane Rubber product and identical lacquer and wax and silicone relaease agent. That time it released very nicely. This time it also released generally very well but there were a couple areas where it stuck fairly firmly. Luckily it did no damage to the master, but in the flat "window" area at one end where the finish was not as good as the pattern itself there was some strong adhesion that pulled away part of the facing of the plate. Thankfully, that area is very easy to repair. Next time on the other I will use PVA instead of spray silicone which I thought would be enough of a release agent. And I will wax, PVA, wax. I will apply the PVA with an air brush to avoid brush marks. The rough seen in the closeup hopefully will not nhibit release from the Repro. If it does, I'll just start over on the urethane.

It is possible that I missed arease with the wax. But I thought I was careful and did 2 or 3 coats.




I have to wait until later next week to do the other side as I have contacted a rubber stamp shop to make some lettering for me. They use a CNC/Laser device to expose a UV sensitive liquid to microdots of UV light to additively form letters of any size and font imaginable. To make "Foster" in bold arial 1.5" high and 1/4" wide will cost 10 dollars. I'll see if that material will owrk well for this mold by making a small test piece. If it is acceptable, I'll get a few more words and place them on the pattern and mold the second side. I have had a very difficult time find appropriate-sized plastic lettering with tiny train modeling letters available and then 1/2" and larger sign letters available . But, the approximately 1/4 size seems very scarce.

I'll try the Repro on the present mold this afternoon.


Denis

 

Got my nerve up and filled the mold with Repro. Per Kelly's recommendation I did test the Wax, Wax, Wax/PVA/Wax release agents. On the left side of the test setup I used the w,w,w,PVA,w routine and on the right added a couple sprays of silicone. The added silicone did help with release. But, there is a concern about the release. When I tested the blobs of Repro dropped onto the mold material, the way it was pulled off tested mostly its peel strength. But as I remove the Repro from the mold, much of the stress on the interface of mold and Repro will be sheer with some peel due to the flexibility of the urethane mold. I am anxious to see how this casting releases.

Here are pics of the general setup:

Testing Wax, PVA, Wax on left and same +Silicone on right

The general setup and release agents. I leveled the mold pretty carefully.

Cross pieces are suspended on short blocks and have drywall heads well down into the Repro. Leveling shims below the mold.

Pretty closs to right on this relatively low-sensitivity carpenter's level


Another view of cross pieces. I intend to wedge under them to break out the Repro, hopefully, without cracking the Repro.


Denis

 

OK! The Repro pattern is out and it and the mold are intact. As you might guess it took some careful application of extraction force---not too much and not too little (as if I knew) and hearing a bit of a peeling noise and seeing a corner come up and then going to the next cross piece and so on. I am glad that is over.



You can see that the mold had some minor imperfections. But it will take only a little hand work to make it cast-worthy. Next mold will be better! Next casting will be done more confidently---I hope.

The Repro casting was still a bit flexible and was somewhat warped longitudinally due to my extraction forces. I just set it on my mill table face-down with some weights for an overnight rest as the Repro finishes polymerizing. In the morning it will be very hard and no longer easily deformable. Also I hope it will be pretty straight. Any lack of straightness will be remedied on the matchplate, however.

Lesson learned: Next time I'll put in more cross pieces, probably five, and the first one will be right on the end. That is the natural spot to begin extracting the casting. I will pull the Repro at about the same curing stage next time. It was hard enough to not dent with my fingernail even with some pressure. But I could tell it was still a bit flexible. That is supposed to be the ideal stage for drawing. The Repro does not heat up very much at all while curing. It is a filled polymeer and the fill material may spread out the resin and add mass and thus reduce heating. Epoxy this thick would have been very warm---probably uncomfortably hot.

Next steps: I've got more urethane on order. Will make the back half mold after I get the lettering situation handled.

BTW, it took just over a cup of Repro to make the pattern piece.

Denis

 

Just curious, how many times would you be able to to mould up flasks from the original wooden pattern before it wears out? I have only ever cast one off's or a few at most. Is a good woooden match plate pattern like that one you made only good for 10-20 moulds, or is is reasonable to get a hundred or thousand moulds from it?

 

I have a couple wood patterns I have used in green sand on the order of a hundred times. I really have not counted. But, considering failed molding attempts, they have likely been used over over 100 times. In that time they have undergone numerous tweaks with improved filleting, replaced lettering, repainting etc. With reasonable care and a little maintenance, a wood pattern should last nearly indefinitely. That is the sort of durability I would expect if it is used with care. One of the reasons I started casting myself was the rough use my patterns experienced in a commercial foundry. There, the person ramming them up is most interested in getting the job done and they are using a resin-bound sand like Airset which solidifies very firmly. Removing a pattern from a resin-bound sand can be pretty hard on the pattern if not done gently. Green sand is so relatively weak that it does not require more than very gentle extraction force.

The plastic clones should be even more durable.

Denis

 

Denis

Thank you so much for your wonderful documentation and photos. Your effort, work, and attention to detail is really quite impressive If you mentioned it earlier, I must have missed it, but I was quite shocked when I read that you cast it in iron