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Earlier runs often better than late runs

Andy Carlson
 

I mentioned once years ago, to my friend Terry Wegmann, that I was looking to get 2 of my most favorite kits of all time--the Bill Gould 4-course tank cars.  I told him that I was only going to purchase kits boxed and sold as Gould kits, as I felt that the parts cast and offered for sale from Tichy to have been cycled more times than earlier runs and was troubled about parts quality. I was half expecting Terry to give me his "are you crazy" response but Terry was in full agreement with my reasoning.

He mentioned an extreme example of later shots from tooling suffering over time was the Cal Scale plastic AB brake set. He said that the mold face of the two tool sides would degrade enough that flashing was getting too severe. Cal Scale's solution was to surface grind the meeting faces to solve the flashing. This repair was apparently done more than once, and Terry said that he could identify what generation of brake shots he looked at by how far from cylindrical the air reservoir component deviated.

So to me both Intermountain and Red Caboose kits should be better in the older color printed boxes than the later non-colored boxed kits. Though I have to admit I often can't see any real differences in these two brands of new vs. older.
-Andy Carlson
Ojai CA

Paul Woods
 

Without pretending to be an expert toolmaker, but speaking as a mechanical engineer with more than a passing acquaintance with manufacturing methods, I believe there can be considerable differences in the properties of the material used to make injection moulds.  Harder materials can be had, which will last practically forever but require expensive manufacturing techniques such as spark-erosion and grinding, because a milling cutter will barely scratch them.  Even a softer material can be made more durable by surface hardening or hard-plating.  On the other side, there are softer materials which can be machined on a milling machine and polished by hand in someone's garage, but obviously won't last as long.  This would explain why some kits never seem to degrade no matter how many have been made.

Eliminating flash by facing off the mating surfaces of a mould seems like an act of desperation to me - admittedly one which I might be tempted to do if short on funds and the tooling had not yet earned a reasonable return, but I would have my limits.  I have worked on jobs where badly worn fine-tolerance parts such as shafts that run in plain bearings (NOT 'friction' bearings, that is not an engineering term!) were restored to original size by metal spraying (a bit like welding spatter but finer) and refinishing.  Lesser wear can be restored by metal plating and polishing, but both these methods are more costly than simply skimming the mating faces in a surface grinder.

Regards
Paul

NYCSHS #7172

Dennis Storzek
 

On Mon, Nov 11, 2019 at 01:02 PM, Paul Woods wrote:
Without pretending to be an expert toolmaker, but speaking as a mechanical engineer with more than a passing acquaintance with manufacturing methods, I believe there can be considerable differences in the properties of the material used to make injection moulds.  Harder materials can be had, which will last practically forever but require expensive manufacturing techniques such as spark-erosion and grinding, because a milling cutter will barely scratch them.  Even a softer material can be made more durable by surface hardening or hard-plating.  On the other side, there are softer materials which can be machined on a milling machine and polished by hand in someone's garage, but obviously won't last as long.  This would explain why some kits never seem to degrade no matter how many have been made.
I was going to state that, but Paul beat me to it. Over the years a LOT of model railroad tooling has been "soft" tooling, because it's cheap.  The choices are, in order of increasing hardness/durability:

Kirksite (a cast zinc alloy)
Brass
Aluminum
Mold steel (a tool steel such as P-20 used in a semi hard state, soft enough to cut with conventional milling, with no further heat treatment.)
Tool steel (which is fully hardened and then worked by Electro Discharge Machining and grinding)

Kirksite could be cast over metal patterns, same as rubber molds are made. If damaged it is not repairable. 

Brass was a favorite of people who came into toolmaking from engraving. A lot of Grandt Line tooling is brass. It is difficult to repair, due to its softness and low melting temperature.

Aluminium is a favorite for CNC machining of cavities because it cuts easy and doesn't break small cutters. The old Front Range line was completely aluminum tooling. It is slightly harder than brass and more easily repaired by welding.

P-20 was a favorite of the old model car manufacturers. It is easily damaged, but weldable.

Tool steel is the gold standard, and welded repairs should be undetectable.

While there are surface treatments that can be applied to give a more wear resistant surface to most of these mold materials, the problem is, in our world, most damage is denting from closing on stuck parts rather than abrasive wear, and surface treatments are ineffective. However, for items produced with quality tooling, the millionth part should look no different from the first.

Dennis Storzek
Accurail, Inc.
 

Donald B. Valentine
 

Dennis Storzek wrote, "However, for items produced with quality tooling, the millionth part should look no different from the first."

I think this would be true ONLY if the person running the molding machine had enough between their ears to know what they were doing, knows what to do when something doesn't seem "right" and knoiws for sure what not to do. having seen even good steel
tooling damaged when a macine was being run manually and soneone closed it too quickly, i.e before the just molded parts had cleared. Not good.

Cordially, Don Valentine
 

dh30973
 

I’ll add my two cents to this discussion. About 13 years ago following his death, I purchased Gordon Cannon’s business of diesel detail parts, Cannon and Company, and continue to run it to date. The vast majority of the molds he created were made old school with a 2D pantograph and small precision milling machine with hand ground cutters in brass. Maybe a dozen were made by someone else for him in 7075 Aluminum by means of CNC machining. The advantage of brass is easy cutting and polishing, with the aluminum being slightly harder in both regards. The brass as Dennis noted is easily damaged by both stuck and partly ejected parts as the mold closes on the part. Repair can be sometimes be done but is tricky. The aluminum is more durable. Some of my brass molds have shot tens of thousands of parts with out any issue while others are getting long on the tooth. A lot seems to depend  on how much draft Gordon included. The ones with very little to no draft are more prone to sticking and therefore getting smashed, while others eject freely. But more draft makes parts with less fidelity, so there is a trade off. 
Apparently the tooling now being done by the big manufacturers and done in China are cut in steel by means of EDM. While those have the capability of millions of shots it is unlikely they will actually ever make that many. Our hobby does no longer support those quantities like the old days of Athearn blue box kits. 

Dave Hussey
Cannon and Company 

Garth Groff and Sally Sanford
 

On 11 November Dennis Storzek wrote, in part:

"Aluminium is a favorite for CNC machining of cavities because it cuts easy and doesn't break small cutters. The old Front Range line was completely aluminum tooling. It is slightly harder than brass and more easily repaired by welding."

Curious. Several of Accurail's earlier cars are a close match for Front Range models.  Were these cars recut with new dies by Accurail, or is the old aluminum still holding up?

Yours Aye,

Garth Groff

Dennis Storzek
 

On Wed, Nov 13, 2019 at 10:27 AM, Garth Groff and Sally Sanford wrote:
Several of Accurail's earlier cars are a close match for Front Range models.  Were these cars recut with new dies by Accurail, or is the old aluminum still holding up?
 
Garth,

They are the original Front Range cavity inserts. 7075 Aluminum holds up well, so long as it is treated gently. Used where it won't close on parts, or drools, or flash stuck to the mold parting line, it holds up well. Not so much if there are sliding shut-offs or other mechanicals involved. There are, of course, five IIRC sets of sides that share a common roof and ends. The roof and ends weren't doing so well, so we mated the sides with steel ends we already had, and built new roofs, also steel. We have built a few things out of aluminum; the 40' plug door RBL and the 40' combo door boxcar sides are aluminum that run with steel ends and roofs. We made the judgement that neither was going to be a high mileage tool. Those taught us that we really weren't saving much, since I'd rather EDM small details in rather than dink around with tiny milling cutters, and if the work is going to be EDM'd, it might as well be steel. Back in the nineties it seemed there was a savings being able to put the rivets in with a .010" diameter ball nose end mill, but the introduction of affordable diamond coated miniature end mills has made cutting electrodes to do the rivets cost competitive, and I haven't done anything in aluminum in years.

Dennis Storzek