I sharpened 5 plane irons for a wood worker yesterday, including two deemed too wide to sharpen by the local tool store. SE-76 handled them all, but all were out of square by a couple of degrees. Squareness was this guys hot button (he brought his own square), so I had to carefully skew each iron in the jig to match his already square edges. What is the point of a Square jig that is not square? More important, how do I fix it? Do I need to tune my jig to fit my machine? Could the truing tool be the culprit?
For the record, I trued the wheel immediately before sharpening. I started with the irons squarely ;) up against the stops. Bottom plate was parallel to top plate, and since these are plane irons over 2" wide there was no question of being tilted in the jig like a chisel can be.
Any suggestions welcome.
If the grindstone is not true, I can never get them square no matter how much I skew the mounting in the jig.
If the grindstone is true, then the only thing I know that will work is application of more force on one side of the tool than the other. I've never been able to get a square end by skewing the mount in the jig.
Perhaps another issue is alignment of the horizontal section of the US bar. If that section of bar is not parallel to the axis of rotation of the grindstone, nothing I know of can remedy the situation.
Steve, my suggestion is to try the recommendation from one Tormek demo. The assumption is, you are starting with square plane irons.
Lower the universal support and draw a line on the grindstone parallel with the bar of the universal support. Then align the edge of the plane iron with the line on the stone.
(http://img19.rajce.idnes.cz/d1902/11/11771/11771137_37021e568ec44478b9ce7dc74d286378/thumb/Line_on_the_stone.jpg?ver=0)
This should replicate the original iron squarness.* :)
Jan
*P.S.: If the plane iron is not square, you will replicate the skew.
Good suggestions.
My oldest metal plane, a very usable Stanley #4 jack plane from 1891, has a lateral adjustment lever, as do planes today. Torgny invented the Tormek. It seems the squareness issue is much older. :)
Ken
Steve,
http://tormek.com/international/en/grinding-jigs/se-76-square-edge-jig/
Watch this video, mount the tool as explained. Use pressure where you need to remove material. If the edge is 90 degree when you start to sharpen, press in the middle, id you see that it starts to move, use pressure on the side where you need to remove more material.
Also, you freehand sharpen, check that the stone is flat. If not, true it before.
SE-76 is a very good and precise jig. Complaints is almost every-time a operator issue :-)
Be sure that the stone is flat and use pressure correct on the tool and be sure the tool is mounted correctly in the jig.
Sincerely,
Stig
May I suggest that you search the Forum using 'se-76' and you will see that there have been plenty of posts about issues involved in trying to attain squareness. My own analysis considered in particular the knock on effects of small angular errors in two planes and had some 3D modelling to prove the point. Also the manner in how the SE-76 was manufactured. Some good analysis was supplied by by Mike Fairleigh.
I seem to post items at the moment where it may appear that I am an argumentative so and so, (it's not intended), but "SE-76 is a very good and precise jig" is subjective as I am not aware of any error or cumulative tolerances regarding accuracy for this jig or indeed the Tormek machines. Similarly Tormek advertising for the T4 claiming "Precision improved by 300%". What precision? How measured? Compared to what?
Staying with the SE-76, after truing up the wheel, I got into the method of continually re-applying marker pen to the surface being ground and checking the grind with a square. If it was not providing the desired solution, I would loosen/retighten the blade in the jig, tweak as I think fit, change finger pressures etc until I get the right answer. The idealistic impression as shown in the referenced video is an infrequent visitor when I try sharpening!
Robin, I have read your thread "Square Edge Issues with SE-76"(http://forum.tormek.com/index.php?topic=1366.msg4173#msg4173 ) and have to say that I fully resonate with your experience and opinions. It is still very topical issue.
I would like to ask you, if you are ready to share with us your 3D drawings dealing with the effects of small angular misalignment and blade twist? If you have difficulties to display the images, let me know the address where they are stored and I will attach them. :)
Jan
Sorry Jan - I deleted them some time ago.
It's a pity, Robin. :(
I have simple 3D CAD software and I am trying to design a model, you had already several years ago. For me it is not easy, I have never worked with 3D solids.
Nevertheless my preliminary results show, that even 1 degree angular misalignment can has significant impact on the bevel squarness. In my thinking, small misalignments we are able to correct by the pressure of fingers during sharpening.
Jan
In the following simple drawings you can see the impact of 1 degree misalignment between the stone axis and the tool in the SE-76 jig on the resultant edge squarness. I have assumed a plane iron 3 mm thick and 50 mm wide, ground with a 25 degrees edge angle.
(http://img9.rajce.idnes.cz/d0903/12/12173/12173769_7c0efa617e3a74cc12713661d917291a/images/Plane_iron_2D_640_1deg_misal.jpg?ver=0)
(http://img9.rajce.idnes.cz/d0903/12/12173/12173769_7c0efa617e3a74cc12713661d917291a/images/Plane_iron_3D_640.jpg?ver=0)
For simplicity I have ignored the hollow shape of the bevel. The bevel was created by a SW milling tool, which is not entirely correct. Maybe this affected the size of the skew.
Jan
P.S.: Please take the figures above only as my first attempt to get acquainted with 3D CAD modelling. In the future I hopefully will be able to prepare more realistic drawings, including grinding stone and hollow shape of the bevel.
I am having a day with many senior moments involved, one of which is that I can't see where I posted the values I used in the 3D modelling!
Thanks Jan - your diagram illustrates the point I had been trying to demonstrate.
Jan's demonstration above shows clearly how seeming deceptively small errors are magnified at the end or the blade.
If Jan's example then introduced an angular error round the axis running along the length of the tool, then a compound error of more annoying output results. This later effect would show different effects dependent on whether this second error is clockwise or anti-clockwise so 'adding' or 'subtracting' to the initial problem.
Thank you Robin for commenting my figure. :)
You are correct, the 3D modelling reveals all the annoying output results, which are consequence of a compound error in positioning the tool against the grinding stone.
Jan
I have used 3D CAD modelling to get an answer to a question: "Can we get a square grind if the blade is twisted?" :-\
Imagine we are grinding with a 25 degrees edge angle a plane iron which is 3 mm thick, 40 mm wide and twisted around the red axis by 2 degrees.
(http://img9.rajce.idnes.cz/d0903/12/12173/12173769_7c0efa617e3a74cc12713661d917291a/images/3D_stone_planeiron_700_bila.jpg?ver=0)
This 2 degrees twist will cause, that we get trapezoidal bevel skewed by 4 degrees in the horizontal plane!
(http://img9.rajce.idnes.cz/d0903/12/12173/12173769_7c0efa617e3a74cc12713661d917291a/images/EXTRUDE_3_3.jpg?ver=0)
To compensate for the effect of the twisted blade we have to rotate the blade clockwise 4 degrees in the horizontal plane (around the blue axis in the first figure).
(http://img9.rajce.idnes.cz/d0903/12/12173/12173769_7c0efa617e3a74cc12713661d917291a/images/EXTRUDE_3_4.jpg?ver=0)
This fully compensates for the skew. What remains is a small change in the bevel width along the edge.
Jan
P.S.: As mentioned by RobinW, when compensating for twist, we have to select the proper orientation to receive the subtracting effect to the initial twist. ;)
Jan, I suggest giving names to the angles to facilitate discussion of them. I suggest b for the bevel angle, so in your example b = 25°. I can't tell from your figure what you mean by the "red axis" but let's say a = 2°. Is the red axis in the plane of the blade? If so then a is the angle between the line formed by the edge, and a line perpendicular to the side of the blade. In other words, if a = 0 then the edge is square to the side of the tool, which is the goal.
If the axis of the grindstone is not parallel to the horizontal portion of the US bar, and the grindstone is trued using the truing tool, then a will not be zero when the tool is mounted squarely in the SE-76 jig. I believe this is the source of some of the problems people have with getting square ends.
Yes Herman, you are correct. :)
The red axis is in the plane of the blade.
If the axis of the grindstone is not parallel to the horizontal portion of the US bar, then they can belong either to intersecting lines, or they can form skew lines which do not intersect each other.
In my understanding the 3D modelling has shown, that some types of misalignment can be almost compensated by simple means. In my modelling I have assumed that the grindstone was square=true with respect to its axis.
At this moment it is not quite clear to me, what we get when we true the grindstone using the truing tool, while the axis of the grindstone is not parallel to the horizontal bar of the US. The truing will probably result in forming some cone-shaped grindstone body.
Jan
Quote from: Jan on December 06, 2015, 10:51:48 PM
At this moment it is not quite clear to me, what we get when we true the grindstone using the truing tool, while the axis of the grindstone is not parallel to the horizontal bar of the US. The truing will probably result in forming some cone-shaped grindstone body.
If the US and the grindstone axis lie in a plane then you will get a symmetrical cone of the type used for ice cream. If not (skew), then the cone is of a different shape. Picture a round funnel with the spout off center. The problem is that as you move the chisel from side-to-side while sharpening you change the bevel angle. You can't compensate for this by adjusting the angle
a, that is, by mounting the chisel in the jig out of square.
There was a thread a while back about a shop teacher with a new T7 who never could get his chisels square. I suspect, but do not know for sure, that this was his problem. The T4 design, again I suspect but do not know for sure, was introduced to overcome this problem in the T3.
If the housing became twisted in the manufacturing process it would result in this problem. I recently bought a new dishwasher with this problem. You could get one side or other of the door jamb plumb (front to back) but not both. It meant that the door couldn't ever close tightly, resulting in water leaks. Had a heck of a battle trying to get the manufacturer to believe me. Fortunately, I prevailed.
Thank you for your explanation, Herman. :)
The effect of a grind stone in the form of a right circular cone could be modelled with 3D CAD SW.
Jan
In the drawings below you can see the situation, when the grindstone has the shape of truncated right circular cone. Its edge is not square, 90 degrees, but only 88 degrees. One side of the grindstone has a diameter 200 mm, while the other only 196.5 mm.
(http://img9.rajce.idnes.cz/d0903/12/12173/12173769_7c0efa617e3a74cc12713661d917291a/images/3D_cone_2deg.jpg?ver=0)
Picture we are grinding with a 25 degrees edge angle a plane iron which is 3 mm thick, 40 mm wide.
(http://img9.rajce.idnes.cz/d0903/12/12173/12173769_7c0efa617e3a74cc12713661d917291a/images/EXTRUDE_4_700_2.jpg?ver=0)
My interpretation of the result is following, when the tool is mounted squarely in the SE-76 jig, we will get almost square end, despite the fact that the grindstone is not square, but conical!
(We have to use the same sleeves and the same US, which were used for "truing" the stone.)
Jan
Quote from: Herman Trivilino on December 07, 2015, 06:28:34 AM
If the US and the grindstone axis lie in a plane then you will get a symmetrical cone of the type used for ice cream. If not (skew), then the cone is of a different shape. Picture a round funnel with the spout off center. The problem is that as you move the chisel from side-to-side while sharpening you change the bevel angle. You can't compensate for this by adjusting the angle a, that is, by mounting the chisel in the jig out of square.
Herman, in principle you are correct, but the change in the bevel angle is negligible. For the situation shown in the drawings (25 degrees bevel angle) it is less than 0.2 degrees for the width of the blade.
Jan
Some days I come here, and see these posts, and I think I am in a classroom, being served a test (solve for *) ;D
Sorry Randal, if it reminds you some unpleasant school experiences, it is not so intended. :)
Jan
Randal,
Your comment gave me a good laugh and made me think. My high school geometry class was fifty years ago, literally in the prior millenium. To put it politely, my math skills most days are less than well honed. After sharpening so many old dull pocket knives in Hartville, I have come to believe there may be a sharp edge in need of honing in this old gray matter. :) Do not lose heart.
At first glance, my simple single piece of wood, the kenjig, seems to have all the technical sophistication of a kindergarten wooden building block. However, the more I use it, the more I appreciate its solid trig foundation. I just reread Dutchman's angle grinding booklet (posted by him on this forum). I confess some of the fine points are still beyond my immediate comprehension, however, I am gaining a grasp of the basics, enough to find it a very useful tool.
I am very grateful for the math expertise Dutchman, Herman and Jan have brought to this forum. I do not see injecting more math as adding complication; I see it as making more things possible. I like Jan's quote, "Iron sharpens iron and one man sharpens another".
Welcome to Tormek 202, Randal. Your wit may be sharper than you realize!
Ken
Quote from: Jan on December 07, 2015, 09:17:51 PM
Herman, in principle you are correct, but the change in the bevel angle is negligible. For the situation shown in the drawings (25 degrees bevel angle) it is less than 0.2 degrees for the width of the blade.
Nice work, Jan. I cannot verify as I find it hard to think in three dimensions. But this is the case for the US bar and the grindstone axis being in the same plane, intersecting at an angle of 2 degrees. What of the more general case of these lines not meeting at all, being askew? That is when, I suspect, the real problems arise.
Yes Herman, I agree with you. I am gathering forces to attack the more general case. Please stay tuned to rethink the potential results. It is really easy to make a mistake when thinking in three dimensions. ;)
Jan
I believe the importance of regular use of the truing tool is under appreciated. I have been surprised twice recently by an out of true grinding wheel. The first time I had not trued the stone in a while, but "it looked OK" to me, a bad assumption. The second time happened shortly after that. I was thinking I had only recently retried the stone, however, this was during the woodworking show when I was using the Tormek extensively.
Not only was my grinding wheel not parallel with the universal support bar, it was also slightly out of round. This is not a product defect; it is a natural product from use. I have since become a twice believer in very regular retruing with very light passes. What normally happens is the diamond tool first removes small amounts from only the high spots, just like rounding a billet on the lathe. Gradually the cutting covers more of the circumference of the wheel and also the distance across. Once a very light cut covers the entire wheel, we are done.
I believe this should be the first variable to be eliminated from the problem equation.
Ken
I have simulated truing the grindstone when the US bar and the grindstone axis are askew. In the picture below it means, that the US bar was rotated by two degrees around the red axis and additionally by 2 degrees around the blue axis. The grindstone trued in this way is conical, its edge is not square but only 88 degrees. The rotation (misalignment) around the red axis has no effect on the conicity of the grindstone.
(http://img18.rajce.idnes.cz/d1802/12/12211/12211533_f3e283fe05b4c4cd26c0f2335ef78494/images/EXTRUDE_3_TRU_RED2_BLUE2_700.jpg?ver=0)
When the tool is mounted squarely in the SE-76 jig, we should get trapezoidal bevel skewed to 91,6 degrees. Surely an annoying output result
(http://img18.rajce.idnes.cz/d1802/12/12211/12211533_f3e283fe05b4c4cd26c0f2335ef78494/images/EXTRUDE_3_SHARP_RED2_BLUE2_700.jpg?ver=0)
This skew can be almost corrected by mounting the tool not squarely in the SE-76 jig, but parallel with the side of the grindstone. In this case the bevel skew is reduced to acceptable 89.6 degrees.
(http://img18.rajce.idnes.cz/d1802/12/12211/12211533_f3e283fe05b4c4cd26c0f2335ef78494/images/EXTRUDE_3_SHARP_RED2_BLUE0_700.jpg?ver=0)
Jan
I love it!
Great effort Jan.
Quote from: Jan on December 09, 2015, 09:13:49 PM
This skew can be almost corrected by mounting the tool not squarely in the SE-76 jig, but parallel with the side of the grindstone. In this case the bevel skew is reduced to acceptable 89.6 degrees.
How can someone suspecting that they have this problem check for it?
Your response pleases me, Robin. :) I'm following in your footsteps.
Jan
I generally view sharpening problems from a basis of my telephone troubleshooting background. Things like careful and frequent truing of the grinding wheel eliminate some of the variables in the trouble equation. As we learn more about what the problem is not, we can focus more on what it may be.
My other factor in viewing troubleshooting Tormek trouble comes from my long hobby interest in machine shop technology and measurement. In simpler, pre digital days, machinists routinely used calipers to measure. A skilled machinist could measure within about .001" with a pair of simple calipers. Using a set of inside calipers to measure the distance between the grinding wheel and the universal support bar would give a very accurate reading of how parallel the bar was from the wheel. By making several measurements along the bar, the flatness of the wheel is also checked.
The beauty of calipers is that there is no actual measurement interpretation, just feeling the drag. I suggest placing a thin piece of paper between the grinding wheel and the caliper leg to preserve the caliper.
Ken
The lessons I have learned from the few examples shown here can be summarized as follows:
A) When after truing, the grindstone is not square, but conical, we will not get square grind for a toll squarely mounted in the SE-76 jig. The cause of grindstone conicity may be a bent bar of the US.
We can significantly reduce the non squarness of the bevel by aligning the longitudinal tool axis parallel with the side of the grindstone. (We have to use the same sleeves and the same US, which were used for truing the grindstone.)
B) When after truing, the grindstone is square, and we are not getting square grind we can deduce that the tool may be twisted or its mounting in the SE-76 jig is twisted.
To compensate for the effect of the twisted blade we have to skew its mount in the SE-76 jig. Using trial and error method we have to find whether clockwise or anti-clockwise rotation of the tool in the jig will compensate the twist. (For more detailed description see Robin's topic.)
Under compensation I understand getting the skew of the grind less than 0.5 degrees. Ideal squareness 90.000... degrees cannot be achieved, when angular misalignments are in play.
Jan
Jan,
I agree with the idea of striving for accurate work, however, I would verify that the tool being ground is straight, parallel, etc. first.
I think it is wise to keep a "known good" chisel in reserve as a system check. If the known good tool can be accurately sharpened, the Tormek is working properly. If not, the Tormek warrents some careful examination.
This idea is a carry over from my photo darkroom days. I would keep a known good negative handy for printing sessions that did not go well. Using the known good negative when needed cut down my trouble shooting time.
Ken
Ken, I have only summarised my recent findings based on 3D CAD modelling. I have had no ambition to provide a checklist to verify that Tormek or the tool is OK for sharpening.
Jan
Jan,
I did not mean to imply that I wanted the Tormek to be OK. Checking the tool first, and/or having a known good tool to test just seems the most efficient way to begin trouble shooting. Let the trouble be where it is. I just want to locate and correct the problem.
Ken
ps Be sure to follow the topic in scissors. Your suggestion to use something thinner in the knife jig works very well with the scissors jig. Good thought!
Why didn't I think of this before? I trued my grindstone today and then measured the diameter on both sides. Outer side diameter: 208 mm. Inner side diameter: 208 mm. I estimate an error of less than 0.5 mm using a steel rule, years of experience, and 60-year-old eyes.
I should have also checked to see if the sides are square to the edges.
Herman,
We might be better served by relying on our sixty year old fingers than our eyes. A traditional machinist could measure to within about a thousandth of an inch feeling with calipers. The actual millimeter or inch reading seems less important to than how the two sides compare.
Ken
If only I had calipers that open that far. I was wishing I had them when I did it.