Reasoning For OR Need For Pre & Polish

Dam I love this board!!!

Fine ....

meanders away mumbling to self

I was hoping someone would say exactly this. My question was leaning toward how one tells if a pre-polish is necessary.

My stones when finished with the 60/90 are very smooth and the shape I want. I then put them through the 120/220 for the smoothing (final).

Does the pre-polish make a difference on how the final polish comes out?

If it does make a difference, then I will make sure I do the pre-polish.

I have received so many beautiful rocks and stones, I do not want to ruin any of them.

I know, I know .... I can always start over with the stones .... but that would mean I would lose more of the stones than I wanted to to begin with.

As always .... I love all input as it gives me more than one frame of reference in which to refer to.

I really love Chuck's response though. I am very impatient (I'm learning) and need to be reminded that with anything that nature gives us to begin with, in my opinion, we need to make sure to not waste anything as it cannot be brought back. All of these rocks are one-of-a-kind.

As always ....

Julie

Hi Julie

I know its hard to wait for the final polish BUT if you want a high gloss finish You just have to go the extra stages As John says abow " you gota lota scratches " to remove

do the 400 G and 600G before the polish and in the end you will be glad you did you did

I do a 24 or 48 hour wash Burnish / wash in Borax and Ivory after the 600 G stage and they come out with a fair shine on them IF not I have a problem

then polishing stage and heres a link to the finished result

img.photobucket.com/albums/v357/john-edward/MaypolishVG010.jpg

img.photobucket.com/albums/v357/john-edward/E-VibeApril2.jpg

Jack
Yorkshire UK

When tumbling the softer types of stone the "prepolish" stage is more important as they will not break the grit down as much during the tumbling stage and therefore the scratches left will be larger and take longer for the polish to completely work out.

With harder stones like agate and garnets etc. they will tend to break down the grit as they go and when left to tumble longer in the fine grit stage, one can "get away with" skipping the prepolish stage and still get a high shine in the polish stage but this is more of an advanced technique that requires some experience to pull off.

In my experience I find I'll still get better results quicker by employing the full four stages. The prepolish stage is the shortest of all the stages usually requiring only 5-8 days so you're really not gaining anything by skipping it.

You will need to let the stones run longer in fine silicon carbide grit and then use more polish and run them longer in that stage to compensate for the missing intermediate stage and you run a higher risk of cross contaminating when you skip the intermidiate stage. You're not really gaining anything unless you're out of prepolish or it happens to be ridiculously expensive compared to the extra power you will be using to roll the barrels that much longer.

The other line of reasoning that supports this is as you tumble the stones, the cutting edges of the grit will become duller and the cutting effectiveness will diminish over time (especially with the softer fine aluminum oxide type abrasives) so depending again on your stones you will have better results when you use a fresh finer grit stage as opposed to letting a coarser hard grit stage run longer. AO is generally around 9.1 on the Mohs scale and SC grit is generally 9.6 so it wears slower which can be good or bad depending how you look at it.

There are other variables that play in too like slurry thickness, which can alter cutting effectiveness. If there is only water in the barrel then the less impeded rock impacts tend to break down the grit faster (and cause more damage to the stones themselves) but as the stones grind, the "dust" mixes in with the water thickening it into a slurry with higher viscosity that will help cushion the load against the higher impact forces by slowing down the rocks just before they impact, preserving the grit for longer and preventing surface impact damage effects on your stones.

Also, the amount of grit you use initially and how much used/how long between the recharges will affect it too. I tend to add 2/3-3/4 of the "recommended" amount of coarse grit to start and then do 1/3-1/2 recharges every 4-8 days depending on the hardness of the stones and keep doing that until the stones are almost shaped the way I want them. The last run through coarse grit I will leave them in an additional 3-6 days to give most if not all of the remaining grit a chance to break down to about half of it's initial grain size so I know I can run the next finer grit without any trouble.

Once you achieve the desired shape you are really only "sanding down" the left-over scratches until they are all small enough for the polishing compound to completly remove in a reasonable amount of time.


Think of it like this, you have a freshly milled solid piece of wood you want to make into a table top or counter top.

If it is straight off the jointer then the surface will be pretty rough but generally flat and the shape you want your final piece to be. Think of this as the "rough grind stage". You can router your edges or whatever at this point (like pre-grinding stones).

Logically, you would want to use the most aggressive grade of sand papaper you have that will result in a finer finish than the current state of the wood in as short a time with the least amount of work required by you as possible.

If you started sanding it with 500 grit paper, you would "eventually" be able to sand it all down smooth but you would burn through a lot more pieces of sandpaper and need a lot more elbow grease before you removed all of the deeper mill marks in it that way.

If you start with a 60-80 grit sandpaper instead, you would be able to work it down to a uniform surface texture in no time and then you can switch over to 120 paper for a quick buff and then 200 for another quick buff and then 500 for another quick buff and you'd have a surface ready to take an oil stain or varnish (the final polish) in less time with less overal effort.

Any finer grits you run after aggressive rough grinding and shaping are to smooththe surface texture of the rock until the polish compound can completely remove the remaining microscopic sized scratches, leaving a surface that reflects light uniformly. Skipping the intermediate stages can result in stones that are technically polished and shiny looking but still exibit the "bottoms" or valleys of the deeper scratches that didn't completly grind out which will surely detract from the finished piece.

Julie,

This is probably not what you want to hear but I even do a step after the "pre polish" 500 grit and with most tumbles, I go a week in 1000, if I am tumbling and an extra day in 1000 if in the vibe.
It is a pain to wait but well worth it!
Fran

Just out of curiosity, and not wanting to upset the barrel at all, why check it next Friday? Why not leave it until Saturday or Sunday, giving it a while longer to do it's work and also during a day (I'm guessing here) where you do not have the stress of work?

You'll have more time to sit and ponder what to do with the stones - onto polish stage or back a stage or two.

Just my thoughts,
John


I'm not lazy nor impatient, but if I leave my stones tumbling longer than 'the book' tells me then it harms neither me nor the stones. In fact I'm only doing in weeks what nature take 100's / 1000's of years to do. Sit down, rest awhile, they'll still be there in the morning.

I think waiting is the hardest part ... So what do I do?, Spend time here reading about this great hobby! Oh, by the way Julie, My final polish stage is set for 3/17 and I can't wait either ...

Too funny!

Right now I can hardly find my washing machine as I have the three tumblers sitting on a big board on top of the washer.

I still have one small (Rolling Stones) and a twin 3 lb Lortone going.

My entire living space is 700 square feet and that also includes my 90 pound Golden named Hope.

I am going though to my first Conejo Gem & Mineral meeting this Thursday and the VP is going to be there early to show the lap lab for all who want to learn and use. YAY!!!!!!!! Now I will hopefully have a place I can go maybe once a week (I don't want to be greedy) to cut, grind, and polish some stuff that I do not want to tumble. I am trying to keep an open mind. ;D

Anyway .... I love all this input ... everyone of you makes perfect sense and I suppose now, I need to keep on honing my patience skills and an open mind. Oh ya .... that and I need to approach that damned wire ... grrrrr ...

As Always .... Thanks
Julie