Offset Grinding Stihl USG, Oregon grinder

[@danielflinn3571]

Thanks for sharing

[@Mightycaptain]

I still grind offset because it changes the top plate angle from 30° to roughly 27.5°. I cut mix hardwood and softwood. Some a little dirty too. So more durable than 30° and sharper than 25°. Between the level of sharpness and level of durability, I'm fairly well satisfied with the compromise.

[@ChainsawUsers]

I am assuming you are using an Oregon type grinder yes

[@Mightycaptain]

@ChainsawUsers yes. 620. Would have rather had the 520. But 620 came on eBay slightly used. Snagged for USD 136.

[@ChainsawUsers]

@Mightycaptain yes I always say do what works for you. Most of my recommendations are just guidelines.

[@ChainsawUsers]

@Mightycaptain I like the 520 but both are good machines

[@rooster3019]

Tinker; I was wondering why you did not point out the difference in pivot points of the chain vise turn table and toward the end you did. With Tecomec design the front of the cutter tooth is, as you said, nearly on top of the pivot point. Stihl probably had to go a different route to accomodate other applications of their universal concept. My chief peeve with the Tecomec is that the degree markings or embossed marks for degrees are not accurate. I use a meter to verify the settings and the straight edge to keep the "tilt" to 0 thus ignoring the decal mark for 0.

[@ChainsawUsers]

@rooster3019 I checked my Tecomec and the back scale was spot on. I have heard people complain saying same as you also. Maybe I was lucky asmine was checked with a digital angle gauge

[@ChainsawUsers]

I just discovered that the Stihl USG grinder has a 17mm offset on the pivot point where the Oregon grinder has the tooth sitting on top of the pivot point. Not sure why they made offset 17mm from pivot point on a new chain. I will make a video of this problem ok

[@rooster3019]

@@ChainsawUsers That certainly accounts for having to correct for the movement of the cutter as it passes along that arc, My two Tecomecs are Joly Evo if I recall correctly and both are similarly off on the abrasive wheel angle and the top cutter angle. It is not a big deal as I tend to set it and forget it. I use CBN disc so wear down of diameter is not appreciable, I get a wild arsed notion that Stihl has considered something to do with table saw blade sharpening, maybe.

[@jeremiahchmielowiec2696]

Do they still sell the fg2 down there? I am having problems getting parts for mine I the USA.

[@ChainsawUsers]

Yes I brought my FG2 Sept 2023

[@elpolaco7654]

I tried, but I guess I couldn't help myself. I lasted quite a long time anyway... After watching your recent videos about the USG and your thesis, I wrote a very long commentary in which I included my understanding of the topic, but it was far too long, so for now I left only the part that interested me the most. I agree with you that the peculiarity of Stihl USG is probably related to it being "universal" and existing attachments. I don't know why you stated in this video that there is actually no difference between the latest version of the chart (K24) and previous versions. In this latest one, of course, the vice is shifted in the opposite direction to the earlier ones, because '1' now means RH cutters. Then there are 2 possibilities: either this last chart is ‘wrong’ or the earlier ones were ‘wrong’ in terms of B-scale settings. By ‘wrong’ I mean one where the B scale setting is not what someone in charge at Stihl intended, because, taking the table as a whole, the latter is certainly more flawed because, having renumbered the left and right sides of the chain, they haven't changed the C scale settings, which means that taking the settings literally ( e.g. -30° for RH, +30° for LH) you will get a chain that is unlikely to cut anything. The settings for the B scale are not critical and therefore someone using the older versions will not have too much trouble, at least when it comes to basic chain types such as Rapid/Picco Super/Micro. I don't want to prejudge what ultimately, according to Stihl, is the standard basic setting, but I think there is a way to judge it. I would do it myself, but I don't have access to a USG: Take a Rapid Super chain, set 40° on the A scale (the third column, 50° of cutting angle). Try sharpening three pairs of cutters (LH & RH) for three B scale settings: (1: LH +15, RH -15; 2: LH,RH 0 and 3: LH -15, RH +15). Check the side plate angle for these cases. The B scale setting for which this angle will be closest (and no less) to 60° (the last chart column) is just the basic recommended setting. By the way, you can check whether the lengths of the LH an RH cutters (what actually matters is their heights and hook angles) are similar in these cases.

[@ChainsawUsers]

Well I have some good news. Someone sent me a USG chart that is about 35 years old 1990, and it does not have the cutters facing each other or facing away from each other. It is stated left hand cutter and right hand cutter in writing on every row. Then, on RM and RS chains, they used 48° top plate angle. They also used 0mm on some chains in the vice B scale. They also used -10/+10 B scale As well as -15/+15 If you leave the still USG B scale set at 0, you automatically get 10° tilt because of the 20mm pivot point offset on scale B -10mm/+10 mm on a USG is almost a netural position in relation to the point of the cutter being aligned with the grinding wheel centre line. -15/+15 will push the cutter 5 mm approximately past the centre line, allowing for miss alingment on the wheel centre line as the wheel gets smaller. By doing this, you get a grind on the gullet that's almost flat. 10° downward tilt will thin out the point of the tooth and give a gullet slope high onto the outside, sloping downward on the inner side of the gullet. The A scale has a 3° error at the horizontal position it's out by 3° tilting downward at the grinder end. Some said it's that way for offset grinding, but that greatly affects hedge trimmer blades with 7° angles One side will be 4° the other side will be 10° Still have been playing with the USG chain for decades and still never getting it correctly laid out, so it is easier to understand. My old version is much easier to interpret and should have been kept this way. There was no information in the user manual. The USG chart has some symbols and numbers and letters but no explanation in writing. It still is a very poor effort who ever is in charge of this document. Thanks for your comments. I always look forward to your comments

[@elpolaco7654]

@@ChainsawUsers Thanks for the answer. Did you maybe get that old chart from YT user sergiysharly3? Wouldn't it be a problem if you shared it? I'm always interested in historical documents, as they allow us to trace the evolution and better understand design decisions. Unfortunately, in these older documents and even patents there are also like in modern ones a lot of obvious errors and probably less obvious ones that I haven't identified. About 30 years ago (1994-95), Stihl changed the design of their "basic" chains, so if this chart is even older, different values may come from that as well. By the way, that old Stihl 'Bars & Chains' manual on which someone handwrote 1990 in my opinion clearly must be older. Based on other Stihl documents, I estimate that it dates from 1981-84. I know you did a similar experiment with slightly different B scale settings, but is there any chance that, theory aside, you could find some time to test in practice how these 3 different (-15,0 +15) B scale settings affect the side plate angle on the Rapid Super?