Hi All,
today I proceeded to turn one of my castings and the oddest thing happened. All went well with the tool part of the turning. When I started wet sanding the blank, which was for a Sierra by the way, the blank literally twisted on the tube. It started feeling as if it was going out of round after about 90 seconds of sanding (400 grit). I stopped the lathe and when I looked it had a ripple in the blank. It looked as if I had held the two ends and spun them diff directions. It even shortened the blank on the tube.
I'm thinking maybe the blank was still just a touch soft. (was a week old) And the glue (med CA) let go enough to let the blank turn on one end. I am at a loss for an explanation. I've never seen this happen.
Any ideas. I have to turn the same blank batch next week for a pretty expensive FP and cant afford to loose the blank.
Maybe cook the blank for a few minutes to harden it up a little.
First, I don't like CA for gluing any blank. I also found it is at it worst on Acrylic blanks. I have finally settled on nothing but epoxy for acrylics, and 24 hours drying time. sounds to me like the glue failed everywhere but at one end. and the acrylic being thin did not take much to twist it.
I actually had a somewhat similar experience with a shredded money blank that I was turning. All went well and I was sanding it down when I noticed that the blank felt different; as if it was out of round and soft. When I stopped the lathe, I noticed that the blank had indeed become soft and rubbery on one end and pulled away from the tube. I only use epoxy to glue in my tubes. I think that the blank had gotten heated a bit more than I thought and that had softened the PR. I set it aside to cool and then I added a bit more expoxy to the end of the blank to ensure that it was attached to the tube.
First of all...I agree...Use epoxy of the acrylics and plastics. 2nd, What size bit are you using?
I was having lots of trouble will the sierras and wall streets till I switched to a 10.5 mm drill bit. It is much tighter and leaves less room for error.
One more question....How many drops activator for each ounce?
I think it was probably more of a overheating the PR problem than a glue failure problem. Been there, done that. Just go slow, use a little water if you want, and don't get it so hot, and it will probably be fine.
First of all...I agree...Use epoxy of the acrylics and plastics. 2nd, What size bit are you using?
I was having lots of trouble will the sierras and wall streets till I switched to a 10.5 mm drill bit. It is much tighter and leaves less room for error.
One more question....How many drops activator for each ounce?
I'm still using the 27/64th, I have a 10.5, I'll try it.
And I use between 4 and 10 drops depending on the weather. Right now I'm on the higher end of the scale, 8-10.
I think it was probably more of a overheating the PR problem than a glue failure problem. Been there, done that. Just go slow, use a little water if you want, and don't get it so hot, and it will probably be fine.
I always wet sand my plastics. I was so early in the sanding stage, I didn't think I could be over heating. I will watch my temps from now on. I think I'm going to try cooking the blanks as well. I don't think this blank was completely cured. And the Sierras are so thin near finish size.
I'm also going to be more careful about assuring the glue is fully set.
Steve 1 week curring is enough for you to turn the blanks, I think you're sanding to hard and heating the blank and melt the glue when you stop the lathe the material shrink because of temperature change and the glue set back again, remember that is not much material on the tube thickeness wise, HTH.
I got to agree on the heat build-up with the sanding. I slowed down rpm while sanding and backed off on the sanding pressure. No more "soft" problems for me since.
I have had this happen with a couple of blanks and can't figure it out for sure. It has happened with PR, Alumilite, and with sewer pipe so it probably isn't the material. The only thing I have done to stop the problem was to use ice water for sanding and to sand a bit slower and with less pressure than I had. I also use CA to secure the tubes and haven't had any problems with that part of it, I use both Thick gap filling and 1500cps depending on what I grab. I like the idea of cooking the blank before you turn it, but I have poured a blank(alumilite) and turned it within an hour of taking it out of the pot with out any problems.
I've turned within an hour of demolding Alumilite too, but it was soft.. sort of
rubbery. I put it on a plate and let it sit on the radiator overnight and there
was an obvious difference after that. Post cure sounds like a good idea..
I did a pour out in the garage(Temp 34 F in Ohio) the other day and used 5 drops per ounce and it went pretty good...I heated the pressure pot up, degassed my pour and brought them in the house under pressure.
Wife doesn't let me pour in the house no more...so sad...
Anyway, I was making pens within 24 hours from those blanks...The outside was tacky but inner blank was solid.
Grub32
ps- Posted pick of this pour in "show off your pens"
I've turned within an hour of demolding Alumilite too, but it was soft.. sort of
rubbery. I put it on a plate and let it sit on the radiator overnight and there
was an obvious difference after that. Post cure sounds like a good idea..
I now have a dedicated toaster oven in the shop for the same reason.
What type of wood chips do you like in YOUR cookies?
I'm rather partial to the 'bolos and the butternut..
I turned one Alumilite too soon, it felt a little like a Toosie Roll.
Post cure did just fine, nice and hard.. THEN the air bubbles showed up!
I can only shake my head..:befuddled:
Most of you are about where I am on this. I kinda felt it was a softness caused by heat. I just didn't know where the heat was from. I actually didn't suspect the sanding. I "thought" i was keeping the blank cool enough just by using water. I'm going to give a couple of the suggestions a try and see how it works. I also had someone PM me and offer the suggestion of using water to heat the resin and aid in curing. Lots of things to try.
I have a special order to make this weekend and can't afford to have any screws ups. The blank is custom cast.
Thanks again all.
Most of you are about where I am on this. I kinda felt it was a softness caused by heat. I just didn't know where the heat was from. I actually didn't suspect the sanding. I "thought" i was keeping the blank cool enough just by using water. I'm going to give a couple of the suggestions a try and see how it works. I also had someone PM me and offer the suggestion of using water to heat the resin and aid in curing. Lots of things to try.
I have a special order to make this weekend and can't afford to have any screws ups. The blank is custom cast.
Thanks again all.
How are you wet sanding? If you don't keep a flow of sorts with the water, it itself can heat up enough to allow heat to build within the resin, especially since the thickness of the resin is fairly thin. Oh yeah, and the brass tube will absorb and retain heat and add to the issue. Sometimes it doesn't take much to soften things up.
An old trick on acrylic motorcycle windshields and shields for helmets is to clean them well then use a propane torch to warm the surface up a bit to get a new "gloss" and help remove small scratches. One had to be very (Elmer Fudd voice here) careful because the line between warmed up and scorched/burnt is a very thin one!!!
