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Measuring small angles, grinding cold saw blades

M. Moore

Titanium
Joined
Jun 8, 2007
Location
Vancouver Island, B.C. Canada
I need some advice on how to measure these very small angles on the teeth of cold saw blades that I sharpen for my own machines.
Currently I am just guessing but would like to know the accuracy of the angle of the grind. (hook angle) The machine does have a reasonably accurate angle gauge but there are a lot of factors and the grinding wheel is curved so it is a bit of a guess. Also the grinding wheel curve is done by hand so it can vary and the teeth are very small on the smaller blades with fine pitch.

I came across a post suggesting the use of a eyepiece magnifier with built in scale and looked into buying one as I think it will do the trick.
My question is do you think that this type of eyepiece will make for a very accurate way to measure the angle and what magnification would be best? There are several choices from 7x to 15x.
I was thinking that a 10x would be good but have to order online so can't test out the product before I buy.

Up until I came across the small loupe style magnifier I though I would have to measure the angle with an optical comparator but now I am hoping that the portable will work as I could just measure it while I am setting up the machine.

The hook angle is also measured in relation to the center line of the blade so I would need that centreline as a reference, which poses some problems with the blade on the machine? Any ideas?

Currently I have two sizes of blade that need sharpening, 11" and 16", tooth pitch ranges from 4mm to 14mm. The tooth height is usually about 1/2 of the pitch length.

Any help would be much appreciated.
 
A magnifier with reticle having angles ought to work. You still may have to do some estimation so it won't be accurate to a fraction of a degree. To get a radial reference line I would make a stub shaft for the center hole of the blade and then mill half of it away. Then a straightedge from center to tooth will give you some reference. And a thin straightedge or you get into focus problems with depth of field.

I'd still have some questions about your process. I understand you're trying to duplicate an existing angle, but you can also work from an angle of your choice. Four degrees works in practice but the cutting edge doesn't last? Try a degree less. If you make notes about what you ground and how it works on your machine you'll have better data than just a measured prior angle

Also, traditionally cutters are ground on the periphery to hold consistent height for all the teeth except for form cutters where it's difficult to duplicate the form. Those ARE sharpened on the hook face, and in that instance the amount removed from each tooth has to be consistent to control tooth height. How are you actually setting up and grinding the blades?
 
TG,
thanks for the tips.
Here is a video of the machine I have, best to mute the music.
YouTube

The grinder is very difficult to set as there are so many variables. It grinds the hook angle and the back of the tooth in one pass. The depth of cut and stroke are done by guestimate and tiny adjustments made until it starts to grind both the back and hook consistently. There are no settings to make a note of as the adjustments knobs have no graduations. The machine plunges down the face of a tooth and grinds the back of the next tooth then repeats. It also happens very quickly even at the slowest speed and there is no easy way to just jog the machine for setting purposes.

This is not so bad if you are grinding all the same size blade but I have two sizes. To further complicate the matter each tooth pitch requires a different adjustment and there is no way to just “go back” to a previous setting. That makes switching from 4mm pitch to 10mm pitch a guessing game as well.
Then there is the offset tooth height which is done for most of my blades, it grinds every second tooth slightly lower, however that setting is easy to make and make a note of as it has a dial indicator built into the machine. The lower tooth has a straight tip and the taller teeth are bevelled and act as roughers.

Once set the machine does do a nice grind and the blades last reasonably well but getting a better hook angle would improve things a bit. Measuring the hook angle while the blade is clamped in the grinder would be ideal and the only way I would want to proceed.
 
I tried to watch the video but it is in in Chinese so could not make much of it, plus I fell asleep. Poor kid was not wearing safety glasses.
Do you dress the wheel? If so, do you dress square or at angle?
Video shows spinning the blade first, likely to make round and have a finish pass with just cleaning up that witness.
Guess I’m no help here, except that often we would quarter the blade to keep it more round/true. that is marking it at about ¼ of the diameter and then make each starting of grinding from the next quarter. This to average the wheel wear

Guess I would make some angle samples with .020 x 1/4 stock of different angles 30, 45 .55 what seems close to what gullet tooth is common on a new blade..then use that to set up the machine..likely would need these going from right tooth to left tooth. might make also some height gauges if you need raise and lower the wheel head...and put a center hole in the wheel holding nut so to be the reference to the height gauges so uou could spot the same height above and below center with the wheel head location. Guess a scribed line would be OK

this is an OK loupe
10x Eye Jewelers Loupe Set 1" Dia Glass Lens w/ Aluminum Body | eBay

youtube The machine running
YouTube
 
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michigan,
Not sure what video you watched but the Baileigh video is definitely not in chinese.
Also it never shows the operators face?
The grinding wheel has a D shaped face, so the bottom of the gullet is rounded.
The entire tooth including the gullet is ground when sharpening.

So you think the 10x loupe would be good for the size teeth on these blades?
 
M.Moore,

There are a lot of challenges for your situation and I wish you well in surmounting them. One is that the machine isn't calibrated in a way that's repeatable, or at least precise enough. For instance, it looks like tooth angles are dependent on the relative positions of the wheel and the workpiece center but you can't accurately set that. Would it be possible to mount an after market DRO on that axis so if you've noted a position for a specific saw you can repeat it? Similar for the vertical tilt of the grinder head but it's not so critical.

There's also the challenge of figuring out what angle is actually be cut on the saw - your original question about using a magnifier. It's an impractical process to make a test grind, remove the saw to check the angle, remount it and adjust position, then repeat until satisfied. It would be preferable to check on the machine but without access to the center reference for a straightedge how is that done? I can think of a couple prospects. Make a straightedge with a suitable notch on one end so it clears the mounting bolt and washer but registers the actual center. Alternatively there are those center finders with two arms that register on the circumference. That tool would also let you check a tooth angle while still mounted but might have problems with the irregularity caused by the tooth gullets.

I guess my preference would be the notched straightedge. You can make a test grind, rotate the saw so it can be checked, then adjust and try again. But for gods sake, if you're sharpening different sized blades and different tooth configurations, find some way to repeatably locate that transverse movement on the machine.
 
QT:[So you think the 10x loupe would be good for the size teeth on these blades?]
Yes every machinist worth his salt should have at least that.
RGs idea of having a DRO so once found the height above or below center is found for one side...then the number can be used for the other side..great suggestion..

Still the height will change with wheel diameter. off center common..but distance changing.

What happens when the D shape wheel get such a large radius that a negative rake occurs? do you re dress by hand?
 
TG,
The saw only travels in and out with the auto grind function.
The tooth position is adjusted manually in relation to the wheel. I am not sure what axis a DRO would go on? Also the tooth depth is related to the wheel diameter so dressing would cause that to change.
After a lot of reading and deciphering the manual instructions I spent a lot of time figuring out how to make all the adjustments on an old blade, it was slow and annoying as I did make some mistakes and broke some very thin wheels. However I persevered and now I can set up a blade fairly quickly and get the machine adjusted to make a proper grind.
The biggest issue is checking the hook angle given the small teeth as described above. My question is regarding the type of magnifier to buy, 10x or 15x?
I think I can figure out a way to have a straightedge reference while the blade is on the sharpener.
 
So you are saying the wheel height position always stays in one position?

There is no right and left rake or difference so a set of the blade teeth?

I would buy the 10x and also buy about a 3" diameter 5x..

10X Magnification Handheld Magnifier Magnifying Glass Handle Low Vision Aid 50mm 887954488005 | eBay

Magnifying Glass 6X Reading Magnifier HANDHELD 2" Glass Lens Jewelry Loupe Loop | eBay

Here find cold saw sharpening, tooth face common but having alternating bevel..Back when I sharpened saw this was called the Atkins grind. YouTube

So yes here the wheel would stay the same height, but the Youtube in post 4 it looks like alternating
 
Michigan,
The wheel head detents and locks in place at 0°.
When tilting to grind the bevels the wheel head is just manually positioned to the scale which is accurate enough.
The saw center line is set by adjusting the saw clamping arbor up or down with a micrometer built into the machine. This allows sharpening different thickness blades which range from 2mm to 3.5mm.
Setting exactly on center is quite important as the saw will cut on an angle if you aren’t exactly on center.
This has required some trial and error and I record the settings in a book for each blade.

There is no set to these teeth, think slitting saw but larger. The blades are hollow ground so get marginally slimmer as you grind them down. I have seen 11” blades sharpened down to 8”.

ok, one vote for a 10x magnifier. That was what I was leaning towards and as you say, useful for other things in a machine shop.

I have been successfully sharpening my blades but looking to improve the process.
 
Sorry, I should have gone back and looked at the video again on machine movements. At about 0:55 they're showing a swing axis that I thought determines the hook angle. There's a scale below but way too coarse to be useful for critical setting. Am I misunderstanding the setup?

For magnification I thought you were talking about something like this. With a reticle like this and a reference line you could see what angle you have. Maybe that's all you need then.
 
TG,
That is correct, the swing axis is used to angle the blade relative to the wheel.
You linked a 7x magnifier, do you think 7x is the best for what I need to do?

I am also wondering if I can use a thin straight edge across the bottom of the gullets which will give me a reference for checking the angle? That should give me a 90° line to center, provided I go an equal number of spaces each side of the measured tooth. That would be fast and easy to do on the machine.
 
Operation
YouTube
company video
YouTube
Best
YouTube

I see the wheel head traveling a straight path from far back to grinding the tooth. With it having the ability to swing up and down for chamfering.
The saw holder (table) adjustment for angle this achieves the distance to the right of wheel center, and distance away for saw diameter. The combination of these allows placing the tooth in position to the left edge of the wheel.
A pawl (finger) that rides an index to locate next tooth with use if of a designate numbed index., that can be set to one tooth or two teeth by length of travel. The two teeth for chamfering alternated teeth.
The tooth hook in made by the small flat of the wheel side after the radius makes full travel. Thar hook or rake angle is made at the result of the of the saw blade being set a Certance to the right of the grinding wheel’s left side edge. The heal or follow can be set straight or to be a radius.

To set up this machine.
I would find a way to travel the wheel head to the grind position (all the way forward). and next clamp a short (1" long likely fine) straight edge to the left side of the grinding wheel…
And then set the finger in the full extended position but not yet touching the index(set away)..
Next to set the saw blade I would clamp a straight edge to follow the saw’s tooth rake angle, the with eyeball adjustment turning the swing are and distance to make that straight edge to be straight to the wheel, and then with the swing arm travel bring a tooth to the wheel. To position the tooth to the wheel set /adjust the finger there.
Wheel straight might be plastic.

I think once you get the feel for eyeball set up you will not even need the straight edges to look over.
*Note the swing arm (table) degrees don't set the tooth rake angle...it (the tooth rake angle) comes from the distance the saw center line is to the right of the wheel's left edge.

'Simple light duty clamp
https://www.amazon.com/Jorgensen-32...992811&sprefix=spring++clamps,aps,189&sr=8-13
 
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For much of cutter grinding the use of straight edges is very common for manual grinder setup. Often grinder hand will look across the machine to an I beam or the side of a tool box to see vertical or hold his pocket scale to see horizontal, then rough or eyeball a something to the near position..it is a simple skill but very handy.

TC grinder machines have so much adjustment trying to go buy angles is a wast of time. very often better to eyeball to close and then begin checking.

Often one will eyeball to close then come in with wheel to male a tickle grind and the bump a little this way or that to match original grind ..and then check for nearness to spec or print..

The fact that most angles are compound makes setting to angles difficult.
 
michigan,
All good info but I am not having any trouble setting the machine and grinding blades.
I merely asked about checking the grind angle with a small magnifier and which magnification would be best for my needs because I have never used one before.
Once I can check accurately I will be able to adjust the dressing of the wheel with more confidence and predictable results.

I have been using CNC sharpened blades as a guide to setting the machine but it is still difficult to compare the results because the teeth are small and it is hard to measure and an eyeball comparison doesn't really work.

So to REPEAT- I am looking for feedback on which magnifier to get, 7x, 10x or 15x?
 
You asked/stated…..
Currently I am just guessing to know (hook angle)
The machine does have a reasonably accurate angle gauge
Any help would be much appreciated.
The grinder is very difficult to set as there are so many variables.
The depth of cut and stroke are done by guestimate and tiny adjustments made until it starts to grind ….
there is no way to just “go back” to a previous setting.
if I can use a thin straight edge across the bottom of the gullets for angle

These sound like good logical questions/concerns...

It seems you have all the questions and you are not even considering what I am trying to explain.
Can you walk up to your machine and set it for an 11” 280 tooth blade(or whatever), with a 10* hook.
In about 5 minutes? That is what I am talking about…but you seem not interested.

Re: QT you... [So to REPEAT- I am looking for feedback on which magnifier to get, 7x, 10x or 15x?]

A simple square head protractor and a 10 power will make gauging the tooth rake easy.

Sorry! Something went wrong! the protractor.
Sorry! Something went wrong! mag glass 1
https://www.amazon.com/Handheld-Mag...words=magnifying+glass&qid=1588077247&sr=8-37 mag glass 2

You set the blade flat on your bench. set the protractor on top of it (the saw blade) with the protractor blade eyeball to the center of the saw hole, eyeball the protractor to be straight up, tilt the protractor head with looking through the glass and see the angle...This will get + - 1/2 degree and that error is standard/allowed for such a cutter(saw blade).
If needing more accuracy draw a vertical line on the bench top to better see/eyeball straight up.
 
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But wait in post 13 and on the best YouTube at the time 4:27.
YouTube

Putting on a wheel with no blotter..Danger don't do that..OSHA will will fine you big time..A worker losing an eye will have half your shop..If that is the company YouTube I would have serious doubts about the machine..

*Yes it looks like when setting in-feed you will have your head right in line with the Blow-Up wheel.

wheel abrasive grains are not perfect and so there will be high grains on the side of any vitrified wheel. The hard flange will push a high point to crack the wheel. That crack may not make a sound so you will not know it is cracked and it is likely to blow up at high RPM ..The blotter dents in with a high grain point so eliminated this problem..

Mine ->likely 1:20 wheel will blow up IMHO..so could be the first one..5th or 20th...But will happen.
Buck
 
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michigan,
All good info but I am not having any trouble setting the machine and grinding blades.
I merely asked about checking the grind angle with a small magnifier and which magnification would be best for my needs because I have never used one before.
Once I can check accurately I will be able to adjust the dressing of the wheel with more confidence and predictable results.

I have been using CNC sharpened blades as a guide to setting the machine but it is still difficult to compare the results because the teeth are small and it is hard to measure and an eyeball comparison doesn't really work.

So to REPEAT- I am looking for feedback on which magnifier to get, 7x, 10x or 15x?

well, can you take a picture with an usb camera and analyse it on the computer? (magnification usually is 200x.)
 








 
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