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PSA discs--- 3M vs. Mirka vs. Norton

N

Nate Hawkes

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Jul 21, 2008
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Location
Ivy, VA
First off, I'm a semi-production turner, mostly green wood bowls. I use shop-made soft foam mandrels which conform well to curved surfaces. I go from low to high, starting wherever needed to at least 400grit, sometimes higher depending on the wood species. I'm about ready to make the switch from 3 1/2" velcro discs to 5" PSA discs for most of my medium to large bowls. Larger discs sand faster and are more economical. There are quite a few choices out there for PSA. I'm not completely sold on some of the "extended life" discs that I've used, for a couple reasons--cost, and they do LAST much longer, but don't seem to cut as fast or consistently as when brand new.

What are you using, and why? I've heard good things about both 3M and Mirka "gold" lines. 3M is "stikit gold" and Mirka is "bulldog gold". Both are semi open-coat, non-loading, stearated, aluminum oxide abrasive on lightweight, probably A-weight paper. Mirka also has another product, "Carat" PSA discs, which seem to match the same description, but cost less. Norton makes a "dry ice" ceramic/al-ox disc that is supposed to last a long time, but costs a LOT. 3M makes a similar "cubitron" disc, which seems to be even more expensive.

Who uses what abrasive, why, and what are you sanding (size, shape, etc). There aren't a lot of PSA users out there that sand in the amount that I want to hear from. Thanks in advance!!
 
I did do a side by side test of the Norton Dry Ice, and the blue discs from Vince, on a 3 cored bowl set of Myrtle, same sizes, and from the same log. I do green turn to final thickness, and then LDD soak, then dry, then sand. LDD makes the sanding a lot easier than non soaked bowls. Duration was about the same, or close enough as to not matter. Each set of discs did finish the 3 bowl sets, and they were almost shot by the end. Main difference was the cost of the discs, but the Dry Ice about 2 1/2 times the cost of the blue discs from Vince. I am pretty sure Vince can get you 5 inch discs.

robo hippy
 
Great info, Reed. I've never tried the liquid dish detergent method, but I might have to if sanding is that much easier. I'll have to read up on it. Vince does have 5" discs on his site. I'll have to give a call this week and chat with him.


Nate
 
I would explain the difference to being kind of like wet sanding, but without the water/oil/whatever. The dust comes off like big wet clumpy snow flakes, not like powder snow. Your abrasive discs stay clean a lot longer as well. For any wood that tends to glaze over or be difficult, it makes a big difference. It requires a soaking tub, and you do need to rinse them off. Use cheap brown (kirkland from Costco) soap, not the colored stuff. It will pull some color out of the wood, which isn't a problem unless you do black walnut first. It was developed by Ron Kent in Hawaii for dealing with Norfolk Island Pine. 50/50 mix with water, 24 hour soak, then dry. I have thought about just spraying, or dipping, but haven't gotten around to that yet. It does need to soak in though.

robo hippy
 
robo hippy said:
...It requires a soaking tub, and you do need to rinse them off. Use cheap brown (kirkland from Costco) soap, not the colored stuff. ... It was developed by Ron Kent in Hawaii for dealing with Norfolk Island Pine. 50/50 mix with water, 24 hour soak, then dry. I have thought about just spraying, or dipping, but haven't gotten around to that yet. It does need to soak in though.
Click to expand...

In Ron's original write up of his process, he wrote that he brushed the soap/water mixture liberally over the piece. He did this several times until the wood would not soak in any more of the mix. He then allowed the piece to dry until it was dry-to-the-touch before turning. He used this process with both blanks (before any turning) and rough-outs. At the time of the write up, he was contemplating soaking the blanks in a five gallon bucket of the mix.

My point is that Ron originally saw a lot of benefit from a liberal application of the soap/water mix and hadn't yet tried soaking the wood in a vat. Soaking may be better than brushing the stuff onto the wood, but it appears that brushing provides ample benefits.

Go here for more info: http://www.ronkent.com/techniques.php
 
I just spoke with Vince and he no longer carries the cheaper blue disks. He has a few left in stock but got so many complaints about the backs tearing away he's dropped them.

Dave Fritz
 
I just got off the phone will Vince. He is still selling the blue sandpaper
from 1" to 5".
He no longer handles the pink sandpaper - cera max. This is one
that a few people complained of the backing.
 
Dave F. said:
I just spoke with Vince and he no longer carries the cheaper blue disks. He has a few left in stock but got so many complaints about the backs tearing away he's dropped them.

Dave Fritz
Click to expand...

Hey Gang,
The pink CeraMax discs have been discontinued. Those discs had a Ceramic blend in 80-150 grits and have been discontinued by the manufacture.

The Blue Flex discs offer a premium Mylar backing, grit range is 60-2000 grit , resin adhesive, and are available...they in stock and NOT leaving! These discs are slightly less expensive then the pink and an extremely good value!

Thanks, Vince
 
Nate, I have used the 5 in. psa Mirka Gold for about 20 years now I think. I use it for exterior sanding. Every now and then I try another 5 inch but not for some time. I use the blue Norton pads. Sometimes there is a glue problem in a batch so I keep a can of 3M 77 spray around in case I need to put a bit on the pad when the heat starts to make the paper come off. And one app of the spray will work for many discs. I go through maybe five 320 boxes per one 100 grit box. I do 100 to 320. For inside sanding I have gone to Ryno grip. hook and loop. ( one, two and three inch)I buy a one yard sheet and cut my own discs. Never had a backing failure. Bill Neddow swears by the dry ice discs. Says my choices in sandpaper are OK at best. I think with cutting my own I do 15cents a disc. I need to find a new source for the mirka gold. My guy went up to 26 a box. I have seen them some time ago at around 21. I also keep the worn 5 inch discs to wad around goblet buffers to sand smaller and very straight sided pieces. I screwed a 1/4in bolt into them and cut the head off. Not to dis Vince as I am using up the last of my blue discs but I think the Ryno last longer for what I do.
 
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Thanks everyone for their replies. Kelly, yours is especially helpful. I appreciate the tip about the 3M77 adhesive. Have you ever used 3M's "feathering disc adhesive"? I have another friend who uses it and likes it. Out of curiosity, why do you use a different paper for the inside? Is it the size of the discs?

In regard to the Rhynogrip paper, I used it for a couple years and got very tired of cutting my own discs. I never could find a section of steel pipe that would've served as a wad punch in the size I wanted, and cutting them by hand is a PITA. I can get away with using squares on round bowls, but they tend to catch on the edge of natural edge pieces. I did find them fairly long-lasting, but very inconsistent in the higher grits if I tried to get away with using a piece more than once. I also am not fond of how stiff the paper is; I like a lighter weight backing for sanding, at least on finer grit paper, or I get occasional dig-ins that I never get with the film-backed discs. I just want something that is faster than what I'm doing now--i.e. a larger pad sands more area in the same time. I still use the rhyno paper for sanding boxes and spindles. It is definitely good quality, just takes too long for me to cut discs. My time is at a premium!

I am sorry to hear that the pink Cera-Max discs are discontinued, at least for the coarser grits. I did find that above 150, the grit would peel right off the disc, which is, for obvious reasons, unacceptable. With light pressure, the coarse discs lasted a long time. I use very soft foam and higher speed sanders--2500-2800rpm; I know there is a running debate on speed; I'm not trying to enter or perpetuate it--I just mean to say that maybe my discs lasted because of the lower amount of pressure that I might be using compared to people using harder mandrels and low speed sanders.
 
I have heard of people using a hole saw for cutting discs, and they are available in a number of sizes. The teeth are filed/ground off, and then a bevel sharpened on it. I use some steel pipe and a 2 X 4 between the cutter and the persuader, a 1/2 inch thick piece of plastic, and a 10 iron (10 pound sledge hammer/persuader) to punch through 5 or so layers at a time. Note here, the punch board needs to be directly over a table leg, and not in the middle of the table as the table will flex, and you loose a lot of the punch power. I have also found that the bevel on the die needs to be a double bevel or it will crimp over. I did punch with the abrasive side down. If there is a leather shop near by, some times they will have a clicker press and you can rent time on it. A standard arbor press usually just doesn't have enough meat to it to take a lot of this type of abuse. I eventually figured out it wasn't enough of a savings to cut my own out. The pre cut discs were less fuss on my end.

robo hippy
 
robo hippy said:
I have heard of people using a hole saw for cutting discs, and they are available in a number of sizes. The teeth are filed/ground off, and then a bevel sharpened on it. I use some steel pipe and a 2 X 4 between the cutter and the persuader, a 1/2 inch thick piece of plastic, and a 10 iron (10 pound sledge hammer/persuader) to punch through 5 or so layers at a time. Note here, the punch board needs to be directly over a table leg, and not in the middle of the table as the table will flex, and you loose a lot of the punch power. I have also found that the bevel on the die needs to be a double bevel or it will crimp over. I did punch with the abrasive side down. If there is a leather shop near by, some times they will have a clicker press and you can rent time on it. A standard arbor press usually just doesn't have enough meat to it to take a lot of this type of abuse. I eventually figured out it wasn't enough of a savings to cut my own out. The pre cut discs were less fuss on my end.

robo hippy
Click to expand...



Pretty good idea with the hole saw, but I was worried about it holding up to the constant pounding of a sledgehammer--I was looking for some 1/8" wall 3 or 4 inch pipe to try and do more than 5 sheets at a time. Mostly, I just don't want to fool with cutting anything. Like you said, its just less fuss and less wasted time to pay a tiny bit more.
 
Nate, sorry for the late reply. Was teaching at the New Zealand symposium.
I just like a larger disc for the outsides of pieces and PSA is cheaper than velcro. The blue flex discs are cheaper than Rynogrip last I looked. And you can buy the Ryno cut into discs, just a few cents more per disc. Same folks that sell the sheets also sell precut discs. No I have not used the feathering spray. A can of 77 lasts years. The tips clog and need to be soaked in paint thinner now and again. But if the other comes recomended give it a go.
 
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