Rub Patterns

 

What are they, what do they tell you, and why do you need to know how to rub a cutter? When you hear someone talking about rub patterns what they are referring to is this: First you sharpen a top cutter for any A-5 clipper blade. (I only rub the top cutter on a blade because I know if the top cutter is good then the comb will also be good so why waste the time?) Once your cutter is sharpened you will need a cast Iron rubbing block that you can purchase for around $65.00 or $70.00 from a company called “The Edge Pro” you can look them up on the web. Then rub the cutter on the rubbing block and look at the pattern. Well, there is more to it than that so read on and you will understand.

When rubbing a cutter I like to use the same amount of downward pressure I use when actually sharpening the cutter on a clipper wheel which for me is two and three quarters to three pounds of downward pressure. 

 I prefer to let the grit on the wheel sharpen at its own speed without forcing it to cut by using too much downward pressure. Too much pressure can and will lift the tips of the cutter during the sharpening process giving you a distorted grind which in turn will create a distorted pattern. The profile of the wheel should be ground into the cutter when the cutter is under 2 ¾ to 3 lbs of downward pressure. For the sake of the new sharpeners that may be reading this if you press too hard while sharpening the cutter then the tips on the cutter will start to rise off the clipper wheel and the grind will not be the same as the profile of the taper that is on your clipper wheel and the hollow will end up being too deep.

So when using 2 ¾ to 3 lbs of downward pressure you can actually feel it when the cutter seats itself onto the clipper wheel. Once the cutter seats onto the clipper wheel don’t let it unseat, keep a constant downward pressure on the cutter, you only get a good grind when the cutter is seated flat on the face of the clipper wheel.

Also make sure you release all tension in your body that might be transferred to the cutter. If you have tension in your body or in your hand you will cut a second face into the cutter. If you do transfer tension to the cutter and end up grinding a new face into the cutter then there will be a visible line across the face of the grind dividing the two faces. At that point you have to continue grinding until only one face is left, and the line is gone, but you will never be able to get a good grind until you release all of the tension in your hand and body that caused it in the first place.

I like what Bruce Lee said “Be like water” that means no tension when you are moving. Stay in control, but be like water and your cutter will stay seated on the clipper wheel.  The next thing I found is that the rub pattern will be affected by how much metal you remove during the sharpening process. For those of you who have a Treyco dial indicator thickness gauge this part is easy, just check the thickness of the cutter before you sharpen it then test it again after you sharpen it and the gauge will tell you exactly how much metal you have removed.

You need to remove between 1.5 to 2.0 thousandths of metal to get a good sharpening.  Some will say that this is too much and that you are taking away from the life of the cutter by removing that much metal, but before you jump to that conclusion think about it. The width of a human hair is about 3 thousandths thick, 1.5 is only half of the width of a human hair. That is hardly ruining someone’s clipper blade.

 

 The truth is you are doing them a favor because if you remove the proper amount of metal then the clipper blades you sharpen will cut better, have better rub patterns, and last longer. The bottom line is, if you don’t know exactly how much metal you are removing from each cutter then you are only guessing and your sharpening results will vary along with your rub patterns.

Use the pads of your three fingertips to rub a cutter (index, middle, and third finger) bend your middle finger, and keep the other two straight. Do four figure eights and then four side to side movements and that s it.

On any taper you use the pattern should be straight across the tips with an arch in it giving it the football shape or the frown face pattern. As I have said before only the tips of the cutter do all of the cutting on a clipper blade. Some disagree, but again think about it. First look at the pattern on your top cutter, the rubbed part of the pattern is the only part that actually touches the lower comb of the blade.

 The truth is only the part of the tips that touch the comb can actually cut any hair. The rest of the teeth do not touch only the rubbed part on the tips of the teeth (or the rub pattern) actually touch so if you want to know exactly what part of the tips do all of the cutting on a clipper blade then look at your rub pattern. It is no different than a pair of scissors, if the scissor blades don’t touch each other than it does not matter how sharp your scissors are they still won’t cut any hair until you adjust the cutting edges to rub across each other.

James

 

More on Rub Patterns

 

When it comes to rub patterns I am learning there is more to them than what I first thought. Since I have trained quite a few people on how to sharpen clipper blades I am in a unique position to compare my rub patterns with my students rub patterns using the same clipper wheel. What I have found after rubbing the blades of my students that some of their rub patterns turn out exactly the same as mine, but others do not. For example early on when I first started training people to sharpen I had a student who was left handed and since my clipper machine only turned for right handed people he had to sharpen on it right handed (I have since added a reverse switch). I coached him how to hold the blade, how much downward pressure, how to get forward pressure, how to relax while sharpening, and all of the same things I teach all of my students to get good rub patterns. He did everything perfectly as far as what I could see.

 

 His downward pressure was measured on a scale between 2 ¾ to 3 lbs and he could do it with his eyes closed, his spark pattern was even, his grind lines were even and went from the tips to the back rail, and we measured how much metal he took off each blade between 1.5 to 2 thousandths, but when I rubbed his blades none of them had a good rub pattern on any of them. We put a few of them together and they cut, but they did not cut great. So I took them all apart and re-sharpened all of them myself. This time the rub patterns were perfect and on the same clipper wheel he had used. All that was left to do in his case was to reverse the direction of the motor so he could sharpen them left handed. After we did that all of his blades had a perfect rub pattern same as mine, but some of the other students were not that simple to correct.

 

 It seems like common sense now, but the one thing I learned for sure from that experience was never try to teach a left hand person how to sharpen clipper blades using his right hand, and for the right handed people I have learned never to send them out to sharpen until they consistently get good rub patterns. This all seems so basic when you think about it, but quite a few of my right handed students could not produce a good rub pattern at first even though it looked like they were doing everything right. It takes some coaching to get them to relax their hand (and body) and keep the cutter relaxed flat on the clipper wheel with the correct amount of down ward pressure, and not to go off the edges of the wheel, etc and then to measure how much metal they remove, any one of which can produce a poor rub pattern.

 

 Bottom line, the student isn’t trained until his rub patterns are perfect. I also have found that lighter pressure when rubbing a cutter shows the rub pattern better than rubbing the cutter harder, which is just the opposite of what I had expected. About four figure eights and four sideways movements is all it takes using the index, middle, and third finger tips. Arch the middle knuckle of the middle finger up, and keep the other two fingers straight with light even pressure on each of your three finger tips, you just need enough pressure about 2 ¾ to 3 lbs to feel that the cutter is seated to the face of the rubbing block for maximum contact. If you press too hard then you will spring the cutter and the tips will come up off the rubbing block causing a very bad rub pattern. So be careful you don’t press too hard when rubbing a cutter.

 

The same is true when sharpening a cutter on a clipper wheel don’t press too hard or the tips will come up giving you an incorrect hollow grind. I always use between 2 ¾ to 3 lbs of downward pressure when sharpening on my 24” clipper wheel and it takes 4 passes. I move fairly fast and not slow so it may not take you that many passes to remove the same amount of metal (if you move slower) which is again between 1.5 to 2 thousandths metal removed. To get an idea of how much metal that is I am told a human hair is about 3 thousandths thick so you are not removing all that much metal, but it is the difference between an ok sharpening and a really great sharpening so make sure you always remove enough metal otherwise you will leave an unfinished sharp edge around the tips of the teeth. Under a microscope the edge will look a bit rounded, all of that needs to be removed.

 

I realize many sharpeners are slow to change methods when what they are doing seems to be working well for them, but when you are sharpening clipper blades and you don’t know exactly how much metal you are removing then your work will end up being inconsistent at best. I check how much metal I am removing each day I am sharpen clipper blades. A clipper blade should last a groomer on average 6+ months. Before I start sharpening I use a small kitchen scale to check my downward pressure for between 2 ¾ to 3 lbs with my eyes closed then usually I have to make a slight adjustment to get it right. I count my passes and then measure how much metal I removed on a special dial indicator gauge that I make just for this purpose. Treyco makes a similar gauge that they charge $150.00 for, mine goes for $100.00. Or if you want to save the money you can go to Harbor Freight and get a cheap dial indicator and a magnetic stand.

 

 To use the Harbor Freight setup point the dial indicator pin directly straight down and set the magnetic stand assembly on something like a rubbing block or the top of a cast iron table saw or any flat metal surface. Again pointing straight down let the pointer of the dial indicator push on the top of the metal surface then lift the pointer and slide a cutter under it noting exactly where the pointer is touching the cutter because when you put the cutter back under the pointer you need to place it in exactly the same spot to get an accurate reading.

 

 Once you have the cutter under the pointer of the dial indicator then set the dial indicator to zero. Go sharpen the cutter then once again place the cutter under the pointer in exactly the same spot and you will see on the dial indicator exactly how much metal you have removed. If it shows less the 1.5 thousandths metal removed then you will need to do a few more passes. If it reads more than 2.0 thousandths then you will need to do fewer passes. Less than 1.5 thousandths metal removed will affect your rub pattern, and produce a poor cutting clipper blade.

 

What does the best rub pattern look like? In my opinion the best rub pattern is one that rubs straight across the tips of the cutter with an arch to it. To be more exact the arch should look like the side profile of a foot ball. Bottom line; the rub pattern shows exactly where the teeth do all of the cutting. The cutter is hollow ground so remember the parts of the teeth farther back “that don’t rub” will not cut any hair, only the parts of the tips that actually rub will cut.

 

With all that said there is more?

Yes, it just goes to show that nobody knows everything. So here is what I have learned recently. I was told by some very good sharpeners that a straight across pattern is better than a football shaped pattern? Well, I have gotten a straight across pattern myself a few times over the years and the blades did cut very well. In fact I couldn’t tell any difference in relation to how a blade cut between the straight pattern and the football shaped pattern, so I asked a friend of mine what he thought and his answer was the same as mine. His conclusion was that either pattern was a good pattern so I accepted that and went on, but we did both agree that one was not any better than the other.

 

OK, I had a trainee come to me after that and he brought his own rubbing block with him, but he told me he could not get a good rub pattern off it. He then told me it had been used by another sharpener and that the other sharpener had given it to him for free. My first thought was that the rub block must be worn out if he got it for free? Turns out it was worn out, so the first thing I did was to spray water on it and rub the face of his worn out rub block with a flat 600 grit diamond bench hone from DMT. The rub I got on the face of his rub block from the diamond hone was an oval shape that showed me that the center of the oval was low and also the outer edges of the oval were low as well so no wonder the rub block didn’t work. The only part of his rub block that was still flat was the oval rub pattern itself, everything else was lower.

 

I have never tried it before, but I decided to try and flatten it for him. First I placed it on my 20 disk sander to quickly flatten it as much as possible. Then I “sharpened it” on my true flat clipper wheel through several times of grit charging, then I cleaned it sprayed it with water and rubbed my 600 grit diamond bench flat hone on it again. This time I could not see an oval rub, instead it looked pretty good so I sharpened a cutter and rubbed it and I got a straight across rub pattern! I sharpened another cutter and got the same. So I re-sharpened the same two cutters, but this time I rubbed them both on my rib block and I got the football pattern both times, So you guessed it a I re-sharpened the same two cutters and rubbed one cutter on my rub block and the other on his. My rub pattern was football shaped and his was straight across. It didn’t matter how many cutters I sharpened the results were always the same. To say the least this revelation changed the way I look at rub patterns.

 

 I then decided to continue to hone the face of his rub block with the 600 grit diamond flat bench stone, then after I was satisfied I could not improve it more I switched over to a 1200 diamond flat bench hone and rubbed it some more till I felt like I could not improve it any more. I then sharpened several cutters and they all now had the same football shape I was accustomed to seeing, no more straight across patterns, only the football pattern, and that is what this person is still getting. What this tells me is that the rub block is a variable when it comes to rub patterns, when the rub block is true you get a football shape pattern, and when the rub block is starting to wear slightly then you may get a foot ball shape or you may get a straight across pattern depending on how you rub the cutter on the rub block.

 

So what’s the bottom line now? Well, it turns out since the rub block is a variable that produces different rub patterns on cutters from rub block to rub block that unless you know for certain your rub block is true flat you cannot depend on it to tell you the condition of your clipper wheel. It used to be when a rub pattern went bad we would all say that the clipper wheel is bad, but now I know you could be getting a real bad rub pattern and still have perfect cutting clipper blades. It used to be all of the attention went to the clipper wheel as being the problem when the rub pattern went south, but now the first thing in my opinion to check would be the rub block.

 

The rub block can easily be checked using a 600 grit diamond bench flat hone. Spray your rub block with water and do circular rubbing motions all across the face of your rub block and it will reveal the shiny high spot and the duller looking low spots. If you have this going on then your rub block is wearing out and it needs to be flattened before you go and have your wheel resurfaced. You can use the method I outlined above using a true flat clipper wheel with 180 grit. Keep gritting your wheel until it looks as flat as it is going to get, then finish off with the 600 grit diamond, and the 1200 grit diamond flat bench hone. This works so don’t be afraid to do it. You will be able to plainly see when your rub block is true flat again after you use the diamond flat hones. After that if your rub pattern is a football shape then you know your wheel is OK. If your pattern is still bad then it is no doubt the clipper wheel, and it needs to be resurfaced.

The bottom line to all that is; If your clipper wheel is good then your blades will be good regardless of what your rub block says. First make sure your rub block is good then you can use it to check how good your clipper wheel is, and you won’t go wrong wondering what the problem is.

 

James Hammons

www.acesharpening.com