What are the best abrasive belts for your sander?
I want to tell you from the first line, there is no answer because it would be like asking which is the best steel.
I wish there was an answer so I would avoid throwing money when I try different tapes that maybe are good tapes but not for what I am looking for, for the way it removes metal or wood,etc.
The category Flexible Abrasives includes abrasive cloths, abrasive papers,abrasive films and non-woven articles.
As a knife maker then consider that abrasive belts are used for many purposes;
Sanding steel, sanding wood, brass, synthetic materials such as G10 and Micarta and acrylics, polishing and sanding and the list is long.
So to say that a tape is the best would be really naïve because it is the best to do what?.
If at the various applications you consider that there are at least a dozen manufacturers, test methods, personal opinions on forums, etc. and you are already understanding that choosing the best tape becomes complicated.
I trusted the advice of a couple of CIC masters and then I started to get my experience but in my research I saw the differences and I still want to try to help clarify the basics to understand some terms and applications of some tapes.
Flexible / coated abrasives construction
On the canvas or paper is laid a binding base of resin, on which the bases of the abrasive grains are drowned, then a second layer of resin anchors the grains to the fabric definitively and determines the seal of the same.
In addition, we can have additive elements, such as coolants, inserted into the second binder or put superficially as a third layer.
Let’s start with the abrasive material that is used on the tapes.
These materials are mainly mineral and have a hardness.
The hardness of the mineral is measured on the Scale of Mohs ranging from one to ten where the first mineral in the series is talcum,the last the diamond.
The Mohs scale provides a purely indicative value of hardness, as the real difference in hardness between two successive minerals also varies greatly.
For example, corinth (No. 9 of this scale) is about six times harder than the topazio (No. 8), while the diamond (No. 10) is about 140 times harder than the Corinthian, as evidenced by the experimental tests of the mineralogist August Rosiwal.
The hardened steel is located between 7 and 8 on the Mohs scale, so logically to remove the steel we want an abrasive with a hardness greater than 7.
Silicon carburo, aluminum oxide, zirconium oxide and many others are hard enough to cut steel.
To make a tape, the abrasive material is tied to a stand.
This support is usually in:
- cotton or
The basis of flexible abrasives is therefore made up of a support, where the most common is canvas or paper.
The material and thickness of the support make it suitable for different uses.
For example, elastic and lightweight straps are suitable for using slow ribbons to shape handles and in elements that need to be rounded.
The heavy support is great for shredding and coarse grinding.
Common Cloth Support Weights:
- J weight/weight is light and flexible
- X weight/weight – medium hardness, standard thickness (moderately heavy, standard thickness)
- Y weight/weight = rigid, inflexible (heavy, less flex)
A heavy Y stand is great for tearing steel, but a bad choice for the soft straps you need to make a curved handle.
For working with more “smooth” tapes, the J weight support is much more flexible and better suited to curves.
Note that cotton, polyester or polycotton joints have different textures, commonly recognizable by the following acronyms:
J – light cotton
JF – lightweight flexible cotton
X – heavy cotton
XF – heavy cotton flexibilized
Y – heavy polyester
YX – heavy mixed polyester
FF – flexible light polycotton
Cards are identified with the weight of the support:
- from Weight A, the lightest,
- to Weight F, the heaviest
On the back of the supports we can have a holdthat determines particular characteristics, such as wet resistance (waterproof ).
Friability is a measure of the ease with which abrasive materials fracture or break.
It’s hard to find specifics on friability, but you need to be aware of the term and you usually want low friability abrasives for steel.
Some materials such as ceramics come off and become sharper when working hard.
Some straps are directional which means they are meant to move in only one direction.
An arrow on the back of the belt indicates the direction of travel.
The absence of any arrows would imply that the belt is bidirectional,which means that it can move effectively in both directions.
The binding agents are the “glues” that hold the abrasive particles on the stand.
Manufacturers have their own proprietary formulas for bonding.
This becomes important if you work with the tape under certain conditions.
Wet sanding and polishing requires a waterproof bond.
Most makers use a 1 “x30” sander/sander, a 2 “x48” or a 2 “x72” or in some cases a manufacturer uses the classic 4 “x36”.
In my experience, size 1 “x30” and 2 “x72” offer the widest choice of abrasive options.
With these measures you will find abrasive tapes in many online stores and in specialized stores where most of the supplies are in sizes 1 “x30” and 2 “x72”.
Main tape types:
In Europe, the FEPA standard provides for the classification in Macrograne from P16 to P220 and micrograne from P240 to P2500.
Also known as corundum or simply referred to as AO.
This abrasive is that familiar rusty brown color.
In the form of the tape we see almost all the dimensions and the grit is made with AO.
AO straps are generally specified in P-grain numbers and the most familiar are 60, 120, 400, and so on.
It’s the most popular type; for characteristics and costs is the most used in roughing and finishing operations of all surfaces of any material.
It has a little sharp grain, but it is very tenacious.
Recently, crumbly grains with better removal characteristics, known as ceramics, have developed.
Also known as carborundum,this abrasive is dark gray or black.
They are not so common ribbons, but it is easier to see them as sheets of damp/dry sandpaper for industrial and automotive applications.
Often called Zircs, they are a good choice for working recooked steel and other metals.
The zirchi generally have a heavier support and come in lower grain, from P36 to 120.
I like to use them for roughing and profiling before heat treatment.
Abrasive life is good value for money.
They are usually blue/blue but in some cases they are also green.
Normally available from P24 grain to P120 grain
More aggressive than aluminum oxide, renew your cut more easily.
Recommended for more removal work on Stainless Steel and Aluminum
The ceramic straps are coated with an extremely hard man-made abrasive.
In some cases these ceramics approach 10 Mohs (hard as diamonds).
Ceramic belts offer a long service life and are able to abrade very hard materials such as hardened steel, titanium and stone.
They are a recent category of abrasive grains, mainly used for the rapid removal of ferrous materials.
The “controlled” fractionation of abrasive grains maintains a high removal capacity for a longer period.
More fragile and sharp. It is not used much in the knife shop as ribbons but it is easy to see it on sheets of abrasive paper.
Used mainly for sanding glass, plastic, marble, wood, brass and wet bodywork.
Structured Abrasives or Agglomerates
Structured abrasives are not so much a material, but rather the way the material is laid out on the strap.
We often see cross-cross patterns, pyramids and other engineered shapes on artificial abrasives.
Like ceramic straps, these are able to abrade very hard materials.
These straps are commonly specified in microns and will have A in front of the numbers.
For example. A45.
See the Micron to P grit table for approximate conversions.
They are part of this category of abrasives of the latest generation having a more or less symmetrical structure of abrasive granules, held by binder and anchored on the supports.
Very long tool life and removal and constant finish throughout the life, with preferential use on automatic machines.
Air conditioning tapes such as Norton’s Vortex and 3M’s Scotch-Brite are suitable for creating brushed effects on the steel surface.
The conditioning tapes are very expensive but fortunately last a long time because of the limited task they perform.
These range from raw to very fine.
The conditioning straps do not have grit values per se but are defined as coarse, fine, very fine, etc.
The cork straps are loaded with abrasive mixture and used for polishing.
The “grain” or grit of the tape depends on the applied compound.
Some manufacturers have a green ribbon (green compound) and a red ribbon (red compound).
They do this to use the same abrasive compound on one color and other abrasive on the other cork to avoid contamination.
Of course all the straps end up being contaminated with steel particles and need to be replaced.
Leather ribbons are perfect for sanding very fine edges.
These tapes can be used dry or loaded with abrasive compounds.
P Grit and Microns
Many of us are familiar with good old 100 grain paper.
The grain size is FEPA (Federation of European Abrasive Manufacturers), sometimes simply called “P”.
This tells us how gross or fine the abrasive is.
A higher number indicates a finer abrasive.
The P-grain uses particles that have passed through a screen.
A P40 screen has 40 apertures per linear inch, and the particles passing through the screen are about 1/40th of an inch.
When working with textured abrasives, there is no “grit” per se.
Instead, the abrasive coating is a certain diameter of particles measured in microns.
A micron = 0.0000001 by a meter, so the two measurements, one being imperial and the other metric, do not lend themselves easily to conversion.
Here’s a useful scale that shows how familiar P-grain and microns are.
Everyone develops their own techniques and will use the tapes in their own way over time.
Here are some tips they gave me to me and from my experience.
You may want to start here and explore different tapes, manufacturers and speeds that work best for you.
- Roughing, a coarse removal, contouring (shaping profiles), primary conical cutting on steel. Alumina zirconium – grain 36 and 60
- Finer sharpening, thermo-conditioned hardened steel. Ceramic – grain 60 and 120
- Very fine sanding, heat-treated steel, brushed stainless steel. Structured abrasive
- Brushing on stainless steel and coarse polishing. Separation straps, from coarse to very fine.
Tape usage speed
There is no basic table of the speeds of use.
The experience gained leads to identify the critical issues of the individual removal and finishing operations.
Generally an ideal speed is identified in meters per second (m / s), but which can vary significantly depending on the different conditions of use;
Using a lot or little working pressure significantly changes all the parameters, affecting the optimal conditions of use; the same applies to more or less oxidized/resin surfaces and to the beginning or end of the useful life of the abrasive.
The speed of tape travel is typically indicated in Surface Feet for Minute (SFM or SF/M).
This is the speed at which the belt moves and removes the complications of the engine RPM, the size of the drive wheel and so on.
Example: The maximum speed on a grinder with a 1800 RPM motor and a 5″ drive wheel means that the belt moves towards 2355 SFM. If you use a 1500 RPM motor and a 6″ wheel you get the same value of 2355 SFM.
The same 1800 RPM grinder with 6″ wheel will work at 2826 SFM.
Then you can play with engine RPM and wheel diameter.
Manufacturers of abrasive tapes recommend speed and are not interested in the particular configuration of the machine.
To calculate your grinder’s SFM, you need to know two things: the speed of the engine in RPM and the diameter of the driving wheel.
RPM = 1500
D (diameter) = 6″
pi = 3.14
Multiply the RPM x D x more…
1500 x 6 x 3.14 = 28,260
Then divide this number by 12 to convert from inch to walk…
28,260 / 12 = 2355
SFM = 2355
In Europe, most AC motors run at an unladen speed of 1500 RPM or 3000 RPM while in the USA these are 1800 and 3600 RPM respectively.
The nominal values of the engine RPM are at load conditions and are always lower than the RPM when empty.
Here is a handy table I’ve prepared to help you calculate the SF/M for your setup:
For coarse-grained tapes, the very fast speed is ok but for thinner tapes and polishing tapes the lower speeds work better.
If you have the ability to control the speed of the sander with an inverter , this can be very useful not to say fundamental.
As an initial starting point we could identify these general thresholds:
- Metal generally: 35/40 m/s
- Stainless steel: 25/30 m/s
- Brass: 40/45/m/s
- Aluminium: 25 m/s
- Iron: 40 m/s
- Glass: 10/15 m/s
- Plastic: 20 m/s
- Wood: 15/20 m/s
- Titanium: 8/10 m/s
But do you understand that it depends on what you are doing? What grain are you using? What hardness does the contact wheel have, etc.
These are indications that can have a value to start trying but you need to find your way to work based on your sensitivity.
For example, do you work on an inclined plane, with a Jiu, with a support or like me freehand without support?
You have to find your way to work!
The choice of accessories for the use of abrasives is very important.
Let’s not underestimate them, they could give us some great surprises.
Basic parameters are:
- Rubber or Vulkollan contact wheels of various hardnesses for ribbons
- Plates or rollers of different consistency for velcro discs (personally I do not use them for knives)
- Inverter for the optimal choice of speed of use, also considering the different cutting capacity between new and partially consumed abrasive.
Which tape to buy?
Again, this depends to a large extent on the material you are working with, but as a suggestion a typical starting order for creating knives that I recommend is as follows:
1 – Zirconia Alumina P36
2 – Zirconia Alumina P60
3 – Zirconia Alumina P120
4 – Ceramic P120
5 – Structured A45
6 – Structured A30
If you plan to still smooth your bevels after heat treatment, I recommend using a Ceramic P60 instead of the Zirc 60.
If you have extra money, buy a finishing strap to polish the steel those with the A as an acronym to be clear.
I hope you now have a little clearer ideas.
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