Resin Casting

[zephyr9900]

Lou, my point is that contact cement wasn't an acceptable adhesive.  Thinned enoguh to brush on in a thin layer it dried almost instantly, and still was susceptible to peeling at the edges.  At this point, as adhesives go, I have been down to JB Weld (possibly thinned) as a last thing to try, but will try your silicone adhesive/sealer.  I haven't heard about that before but will search it out.

David, those are good suggestions.  It puts the adhesive in shear rather than peel around the pin/tab, which is always a good thing.  I will keep that in mind.  Otherwise it's off to work on my oven/hotplate soldering test.

Mike, I don't have that sophistiacated of milling equilment!   To mill the fluting would take a .022-.025 ball-end mill.  Ball-ends do not cut well on thier end, so I would need to tilt the cutter relative to the workpiece to get out a ways on the flutes where there is at least some cutting speed.  With the fluting wrapping around the end of the tail car, that means a 5-axis machine.  And that doesn't address interruptions in the fluting, such as numberboards etc.  And it doesn't address the fine corrugations flanking the fluting and over the top of the roof, which would likely need to be scribed.  I'm not jumping on you--I've just given this some thought already.

What I have thought about is a little "screed" (like a half-round "D" bit) that would have the form of one flute, that I could apply to the etched flutes and scrape them a little more rounded.  I will send you a PM about the high-rez RP.  Thank you.

Randy

[peteski]

I'm no expert but I thought that in N scale etched brass represents fluting quite well. The etching process leaves a rounded trough between the raised corrugations which seems to look similar to the shape of 1:1 fluting.  It probably isn't 100% accurate but it seems close enough.

[Philip H]

Depends on what is being represented with said fluting.  I did a Spanish Barrel tile roof in last year's TRW Square Foot Challenge, using Micron Art etched roof material.  With the seperatings were clean, and I painted it in a way that looks realistic, the trough tiles weren't really rounded.

[Sokramiketes]

Mike, I don't have that sophistiacated of milling equilment!   To mill the fluting would take a .022-.025 ball-end mill.  Ball-ends do not cut well on thier end, so I would need to tilt the cutter relative to the workpiece to get out a ways on the flutes where there is at least some cutting speed.  With the fluting wrapping around the end of the tail car, that means a 5-axis machine.  And that doesn't address interruptions in the fluting, such as numberboards etc.  And it doesn't address the fine corrugations flanking the fluting and over the top of the roof, which would likely need to be scribed.  I'm not jumping on you--I've just given this some thought already.

What I have thought about is a little "screed" (like a half-round "D" bit) that would have the form of one flute, that I could apply to the etched flutes and scrape them a little more rounded.  I will send you a PM about the high-rez RP.  Thank you.

Randy

That's big!  I've got a couple .005" and .010" dia ball ends that I've used, though I stick with Freeman's machineable wax.  It cuts clean and is much harder than candle wax, and I break fewer bits!  I ran an entire side of a Z scale P-S 5344 boxcar in wax as a test with a .010" dia ball end.  This was on a borrowed Sherline converted to CNC by Flashcut.  Run times are long, but doable.

Have you tried a ball end on brass for fluting?  I know there's ways to have a ball end cut better by the book, but the tool guy at Intermountain once told me their .005" ball ends lasted for weeks of conventional milling!  That was on aluminum I believe.  Brass should be easier since it's self lubricating. 

[pnolan48]

I'm a little behind the discussion (so what else is new?) but thought I'd add that my vacuum pot does allow me to use old molding rubber. I'm buying the materials in one gallon buckets and had about 12 oz of each when I left them 2.5 months ago. They were already borderline when I left, and I didn't have any inert gas. But putting small quantities in the pot for 45 minutes removed enough moisture to make the remains usable. Yes, it foams like crazy, so I drop 1 oz containers of material into 7 oz containers and, after the vacuum, scrape out what's left in the 1 ouncers into the bigger containers and mix. I also allow a little extra time to set. It's been a workable solution for me, as I don't have any big hull molds in the near future, so salvaging that last 24 oz saves me a lot of money. I think this does not make the molds any better.

[LV LOU]

I'm a little behind the discussion (so what else is new?) but thought I'd add that my vacuum pot does allow me to use old molding rubber. I'm buying the materials in one gallon buckets and had about 12 oz of each when I left them 2.5 months ago. They were already borderline when I left, and I didn't have any inert gas. But putting small quantities in the pot for 45 minutes removed enough moisture to make the remains usable. Yes, it foams like crazy, so I drop 1 oz containers of material into 7 oz containers and, after the vacuum, scrape out what's left in the 1 ouncers into the bigger containers and mix. I also allow a little extra time to set. It's been a workable solution for me, as I don't have any big hull molds in the near future, so salvaging that last 24 oz saves me a lot of money. I think this does not make the molds any better.

Pete,have you tried Smooth On silicone rubber thinner? I tried it,had great results.It doesn't seem to change the hardened mold in any way,yet it really helps thin out old product...LOU

[zephyr9900]

I'm no expert but I thought that in N scale etched brass represents fluting quite well.

Franky, I agree, Peteski.  Holding up the FNS/PT Pioneer Zephyr bodyshell next to a Kato prewar Zephyr shell, I can't tell the difference at 4", and that is my eyes' natural focus distance.

I've got a couple .005" and .010" dia ball ends that I've used, though I stick with Freeman's machineable wax.

I've machined brass with .009" and .010" ball-end and square-end bits.  Even with 20krpm it is a little scary.  In brass, a .009" endmill wants over 60krpm, and that is at the perimeter.  Towards the middle of a ball-end, it just rubs.

Have you tried a ball end on brass for fluting?

Truthfully, I have not and should, Mike.  But I have seen the difference between perimeter and apex cutting even on a .094" ball-end I used for some F scale spoked driver centers in brass.

One thing I miss about my Sherline mill ( http://www.prototrains.com/shermill/shermill.html ), was that I had the 10krpm pulley set, and being the primary spindle was mounted in nice beefy ball bearings.  My Tormach only goes to 4500 rpm on the primary spindle, and for tiny cutters I use a 20krpm Proxxon IB/e (think Dremel on steroids) mounted on the side of the main spindle, but even though I've replaced its spindle bearing with a ceramic hybrid, it doesn't have the rigidity of the Sherline.

Randy

[Sokramiketes]

Franky, I agree, Peteski.  Holding up the FNS/PT Pioneer Zephyr bodyshell next to a Kato prewar Zephyr shell, I can't tell the difference at 4", and that is my eyes' natural focus distance.
I've machined brass with .009" and .010" ball-end and square-end bits.  Even with 20krpm it is a little scary.  In brass, a .009" endmill wants over 60krpm, and that is at the perimeter.  Towards the middle of a ball-end, it just rubs.
Truthfully, I have not and should, Mike.  But I have seen the difference between perimeter and apex cutting even on a .094" ball-end I used for some F scale spoked driver centers in brass.

One thing I miss about my Sherline mill ( http://www.prototrains.com/shermill/shermill.html ), was that I had the 10krpm pulley set, and being the primary spindle was mounted in nice beefy ball bearings.  My Tormach only goes to 4500 rpm on the primary spindle, and for tiny cutters I use a 20krpm Proxxon IB/e (think Dremel on steroids) mounted on the side of the main spindle, but even though I've replaced its spindle bearing with a ceramic hybrid, it doesn't have the rigidity of the Sherline.

Randy

Time for an upgrade again! 

Actually, try the Freeman's machineable wax sometime.  You won't need the spindle speed and pulling a mold off the wax would be relatively easy. 

[pnolan48]

Pete,have you tried Smooth On silicone rubber thinner? I tried it,had great results.It doesn't seem to change the hardened mold in any way,yet it really helps thin out old product...LOU

Thanks, Lou! I didn't even know it existed. Besides requiring some serious arm muscles to mix, the thick stuff worked fine. I'll include some in the next order, as well as some inert gas. Spent near a week getting my new cutter functioning properly, so I can just now look at what I'll be molding in the next few months.

[Sokramiketes]

Forgot Rule #1, photos...



Fox truck sideframe, cavity milled into machineable wax, resin direct into cavity. 

[zephyr9900]

That is sweet, Mike.  And the extraction handle is clever too.  How many pulls can you get from a mold like this?  I do have chunks of Freeman blue wax, but never considered anything like that.

Randy

[PJPickard]

I have playing with this same idea...but only test parts, nothing "real" yet.  I have trying cavities in delrin.

Can you get away with 0 draft?

What mill are you using?

Paul

[LV LOU]

Forgot Rule #1, photos...



Fox truck sideframe, cavity milled into machineable wax, resin direct into cavity.

 Mike,how tough is that wax? A friend does dental work,he gave me some wax he uses for lost wax castings.I poured it in a mold,it stuck to the silicone like I crazy glued it in there!! I'm wondering if that stuff is any better.I'd like to lost wax cast pewter shells and chassis..

[Sokramiketes]

That is sweet, Mike.  And the extraction handle is clever too.  How many pulls can you get from a mold like this?  I do have chunks of Freeman blue wax, but never considered anything like that.

Randy

You'll get a bunch of pulls from it.  No mold release needed.  I pulled 5-6 copies and then sent the mold to Chris333 who pulled a couple more.  It still looked perfect when shipped back.  And Chris was able to added journals to the first generation castings and cast a bunch of copies of completed side frames. 

This part was pretty shallow at .040" if I remember correctly.  Work in a degree of draft if you can. 

[Sokramiketes]

I have playing with this same idea...but only test parts, nothing "real" yet.  I have trying cavities in delrin.

Can you get away with 0 draft?

What mill are you using?

Paul

That sideframe was cut on a CNC converted Sherline from Flashcut. I got away with zero draft, using a flat end mill on the cavity with a .008 ball end mill on the rivets.  This part was very shallow, so it didn't seem to get caught.