I own 5 Incra T-rules (150mm, 300mm, 6in, 12in, 18in) and I got them primarily to measure with rather than to mark saw cuts. While making setup blocks for my MFT table, I found something surprising — they are all precise but they are all offset by 0.25mm.

In essence, since they take a 0.5mm mechanical pencil, these rules mark a cut line rather than a centered line at the desired measurement… that it is, you can get a full width pencil line on the edge of your work piece if you mark at zero. This is a big pain and really destroys the main reason I bought these tools.

I initially discovered this when I was cutting plywood strips to use as setup blocks on my MFT and measuring each block with an Incra to make sure I had cut it precisely. I was losing my mind because the widths were measuring correctly (center of the hole, lined up with the edge marking) but then combined setup blocks were adding up incorrectly.

Using my 150mm Incra, I measured my Veritas metric setup blocks and found all the pieces to be 0.25mm short (center of the hole at 1/4 mm offset, by eye — it could be 0.01 inches or similar) But then, when combining multiple blocks together, the total would also come up 0.25mm short. It therefore must be the Incra that’s off by some constant offset. This is when I checked the zero line as described above. I also double checked the tightness of the metal strip on each T-rule, verified that I could not shorten this offset, and also verified that the 127mm/5in line drawn was the same across all five of my Incra T-rules.

This is really disappointing to have a cut/cutoff line instead of a centered line. When making precision cuts you are rarely sighting the track saw guide rail off of a drawn line, so my main value for these T-rules was to get quick and accurate verification of measurements on cut pieces. Now I have to constantly remember to look through the tiny 1/4mm offset hole below the whole mm, and there is no reference line on the side of the rule either, so it just looks off. Similarly, if you are drawing lines to place fasteners, you would want a centered line so you can drill where the lines cross. With these cut lines, your fastener placement needs to be on one edge of each line, and you have to remember which edge.

Does anyone have any suggested solutions? Do woodpeckers T-rules have centered lines without the offset? Does Incra have a 0.25mm piece I can attach to get rid of it?

Edit: I forgot to mention that the measurements along the bottom edge of the rule do not share the same offset. It really seems like an oversight in the design.

Edit 2: The design oversight comment is based on the fact that there are both pencil slots in the bodies of the T-rules and also measurement markings along the edge. What I’ve discovered is that the pencil slots will draw you an accurate cut off line, but the edge markings are simply inaccurate because they are lined up with the center of the pencil slot. If this had all been intentional, I would expect the measurement markings to line up with the inside edge of the pencil slot to give an accurate measurement.

It'd be great to see a photo of the T-rule against another ruler (up close, of course) so we can see what you're talking about.

I'm not in my shop right now but I believe if you look at the array at the bottom which is in 1/64" increments on the large T rules you will see that the reference crossbar is centered on the hole at 0/64", which implies that the center of the holes is at the nominal dimension.  I will check later and report back.

All, thanks for the warm welcome. I was a long time lurker and first time poster.

I’m attaching two pictures to show what I mean. One of them shows the cross bar of my 150mm T-rule against a piece of white MDF with a factory edge. You can clearly see the zero mark is centered on the zero hole but the entire zero hole shows white.

The second picture shows the end of my 300mm rule lined up against the cross bar of the 150. I angled it so as not to slip into the rounded edge of the cross bar. You can try it yourself or take my word for it, but you can see clearly that the measurements don’t line up. My conclusion is that all the marks along the side edge of the T-rule are offset and thus can’t be used for measurement. Bummer.

I haven’t reached out to Incra. I’ll do so and report back.

I have just compared my 150mm rule to a vernier mark out knife and another mark out tool along with Veritas set up blocks and I think I get the point the OP is trying to make. It appears the actual measurement is the left side of the pencil mark so if using the mark to cut out to you would need to include the line in the cut. I don't understand what the OP is doing but then I don't have an MFT. If making spacers his method is not really accurate enough for me, a non-digital vernier or micrometer would be far better and wooden spacers are the wrong material. Someone with more insight on MFT's might have more understanding of the whole thing.

Regarding the setup blocks, I’m cutting 620mm long strips out of 12mm ply at various widths in order to get quick alignments of cuts by stacking the strips against bench dogs. I made an offset strip from the first row of dogs to the cut line, and then used the veritas setup bars to make the measured strips.

They are very accurate. 18 of them stacked together looks dead on at 278mm, up to the 0.25mm offset on the T-rule. Probably won’t last forever but they are a huge time saver for a big set of French cleats and shelves.

I seem to be blocked from posting more pics but I’ll give some evidence once I’m allowed.

Edit: pics of the setup blocks:

It looks like the T-bar isn't attached properly. Did you follow the instructions in this video?

https://youtu.be/O-IMyViknVo?t=264

She holds the ruler by the T-bar, with the blade oriented vertically upwards. That pushes the ruler against the raised edge of the T-bar. My guess is you're 1/2mm away, which is probably the slop in the attachment hole.

I’ve redone it a bunch of times. It comes out the same and the issue repeats across multiple different T-rules.

If you watch the video closely, you can actually see she has the same problem as me at the 5:20 mark — the zero mark on the edge is slightly off of the crossbar and there is no red visible behind any of the holes centered at zero.

Yes, mine looks the same.  One thing I have seen over the years with this rule is that the registration of the left edge of the rule to the raised ridge on the left side of the crossbar pretty easily slips to the right.  So much so that each time I get mine out of the drawer to use I reflexively loosen the nuts, push the rule to the left to assure tight registration and retighten the nuts.

As an error check, I measured the setup bars with my digital calipers and they came back at 15.97mm and 15.98mm, so that doesn’t explain the results. I also reset the connection of all five of my rules to their cross bars, and I locked the rule in vertically pressed down into the bar as it shows in the video.

The problem is definitely still there on my 150mm, 300mm, and 18in rules. On the 6in and 12in rules it’s too close to call visually because I can see a hint of red through the pencil slot, and I don’t have imperial setup blocks. However, when I draw a line along a straight edge workpiece at 127mm, it appears to line up with the line drawn at 5in on the imperial rules.

I asked the Incra folks if there is a local dealer I can take it to for verification. We’ll see what they say.

Digital calipers are simply not accurate enough

Yes they are.  We're talking a difference of 0.25mm, on a mark being made by a 0.5mm lead.  You can see that by eye, let alone a caliper.

I’m going to send some pics back to Incra and see what they say.

Mine looks identical to yours.  I expect it's normal, but would be interested to know why they make em that way.

Not that one should have to, but it would seem pretty simple to file 0.25mm off the edge of the ruler that butts against the T-bar.

I may end up having to do exactly that.

One reason I've not gone down the Incra marking path is that at the end of the day, it's just a pencil line on a piece of wood. Unless you're cutting by hand, what really matters is how accurately your cutting machine is setup - and that's independent of whatever mark you made on the wood.

Exactly. I only use the marking feature for laying out non-domino fasteners or as an error check for long cuts that don't fit on the MFT, like when breaking down sheet goods. I'm using an MFT and using the guide rail for my TS55 track saw on a hinge. I have bench dogs fence with stops as well, and I've been able to get pretty accurate cuts on plywood with this setup. The setup strips I was making were just to remove the trial and error element of setting up the first repeatable cut.

This is also why it's so frustrating though. My primary intended use was using the measurement lines on the side of the T-rule to verify the accuracy of my length of cut. Having it be off all the time is irritating, and having to try to sight through the pencil slots in order to compensate is really a pain.

Filing the end off the ruler would have no effect since the ruler is attached to the T-bar with holes.  You'd have to elongate the holes .25mm instead.

I also have a couple of Incra T-rules and find them excellent.
I have not noticed the offset but actually I hope this is true for mine also.
Then, if I cut the pencil line away I know it will be accurate. Brilliant when used together with a tracksaw. I find it easier to cut to the left of the pencil-line than hitting straight in the middle.

I agree entirely, it then becomes a very accurate method of cutting to an exact size. A vernier marking knife is available from Ebay and other sources which can be slightly more accurate.

https://www.ebay.com.au/itm/284893279009?_trkparms=amclksrc%3DITM%26aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D20200818143230%26meid%3D98442f90a26e446aa71fda3da54aafed%26pid%3D101224%26rk%3D1%26rkt%3D5%26sd%3D373772449359%26itm%3D284893279009%26pmt%3D1%26noa%3D0%26pg%3D2047675%26algv%3DDefaultOrganicWeb%26brand%3DUnbranded&_trksid=p2047675.c101224.m-1&amdata=cksum%3A28489327900998442f90a26e446aa71fda3da54aafed%7Cenc%3AAQAHAAAA8Hfu33UHQ7b5PJ8ZY%252FcxAQCcgmlEgIXb%252FwWQEtps2wfnwl2oTNziHDgFfjCOXrLrSZndn1LX4T5np7lWocWcZkATksM8o5ocFveuFYe33s9M0PTAmr2fbJkcrz%252BULG91hSGq2jvaMP6FsRLR6omNeyJUlIVVqiqoL849xLDTPN%252FF%252Bj4vSVjL7GOsXAHB8vYaF9XQJ%252BztEA4rYmMXXFtZfSLUEE0QHe0%252F1gWIVjGOTlErAPXBECCe35ZKMGag0b7Vm7xwFVymruYeDOISghzfExIHjFcFgBjNt91by3yRm9hFSqUSTCxYUL0ShOpeTpthqw%253D%253D%7Campid%3APL_CLK%7Cclp%3A2047675

Update:

I was able to verify the accuracy of all my imperial rules using Kreg 1/4” setup bars and also using the Incra guaranteed square. Only the metric ones have issues.

I discussed everything with Mark at Incra and they are sending me out replacements for the metric rules! Really great customer service. He also clarified that the lines are indeed supposed to be centered on the measurement marks, i.e., not cutoff lines like I was experiencing.

I’ll report back once I get them but it seems at this stage like I just got a bad batch. One potential source of the error is the aluminum cross bar being out of square. Mark mentioned that that can happen with the extruded aluminum, and sure enough the bars are out of square on my two metric rules.