I have one for the EQ and just need a spindle made up to suit. Pretty excited to give it a go for some drawer front work as in this image. I do think it's a less appealing grain appearance than steam or bent lam, but that's not always an option.Originally Posted by Jared Sankovich
I use a 125x55 rebate block with a bearing designed to match it, so it's very close. You may well find the cut with this approach is more than good enough and you won't need the segmented block. Remember though, that shear cut block will give you a mild radiused cut which may or may not matter, depending on what you're doing.
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[OP]
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Aha...I did not think of this, but I suppose it make sense given the geometry of the shear cut. How much of a radius / out of square from the adjacent edge are we talking about over the height of the cutter block? If I cut joinery first and it’s very slightly / barely perceptible I don’t know if it will matter in this case, but that is not something I was thinking about.
Thanks for the post Brent!
Still waters run deep.
I've never measured it, but it's very small. It affects edge joining/gluing (because two of those slightly radiused edges together doubles the difference and gap) mainly, and is hard to even see unless you're looking for it. The greater the sheer the greater the radius. That is, unless the knives are also radiused like in my 16" shear cut Wadkin Jointer. They rarely are with that type of block. The carbide inserts in the segmented heads are radiused for this reason but aren't always perfect for every block diameter/shear angle combination, so sometimes you can suffer from the same problems actually but with multiple scallops across the face.
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Last edited by brent stanley; 01-31-2022 at 4:28 PM.
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If you have meeting joinery coming into the part that was cut with the shear rebate cutter you most likely not notice anything if it’s less than 1 1/2” thickness or so. The 4Z rebate blocks cut about as well as the spiral heads in most timbers. The spirals have some advantages in figured wood. They are usually smaller diameter and useful for tight radius work. They need a lot of rpm and you have to be careful not to overfeed.
I still have a lock edge head with the bearing like Warren showed. I still use It occasionally just because I have a few certain profiles for it. All I can say is I’m thankful for modern tooling and machines.
Sometimes I do curve door jambs with bricklayed segments to avoid any spring back. I have a 5” highX 5” diameter 50 bore 4Z Tersa head for shaping these. Using a inexpensive adjustable dead collar because my Aigner curve hood will not fit this setup we just nibble away at it little by little.usually have to flip the piece over to finish. That head combined with a 50 X 200 mm shaft will do a lot of heavy work. If your doing much curve work a adjustable dead collar will pay dividends.
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The neutral point is typically in the middle of the block, with the deviation getting larger towards the top and bottom. So if you are milling the edge of your piece only on on edge of the block, it will be biased in one direction. If the stock is being milled by the block right in the middle, it's split 50/50. I often use an outboard fence on the shaper for final widthing of repetitive pieces because I can use the power feeder, and I alway make sure it's using the middle of the block for that. Harder to do when pattern milling thinner pieces.
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The distortion from square of a straight insert set in a raked pocket had not occurred to me. I have a pair of 7" diameter opposing shear tenon cutters but they are brazed carbide and ground in the head to cut square. I use an Amana "chiclet" insert head for pattern cutting with the square inserts set vertically rather than on a helix which works well. It sounds as though the insert shear cutter has a minimal downside but you may want to check out the fit on a straight mating cut before investing in a collar and bearing. If necessary the mating areas could be milled on the jointer and left uncut by the pattern cutter, or tuned up with a hard sanding block or block plane.
Philip, have you ever noticed any issues with fit on rabbets cut with your rabbeting head?
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There was a discussion on woodweb a few years ago regarding the shear heads. The ammana heads are very slight shear angles, so less of a convex curved cut, but still theoretically present. I've not noticed any problems and I run all my FF stock with a 2z amana shear head against an outboard fence on the shaper.
https://www.woodweb.com/forum_fdse_files/aw/826856.html
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I think you would notice it if you were trying to edge glue boards off a shear head. If you are doing that a straight knife insert head would be better. I have done many frames for glass panels using the shear head for the rabbit and the same head to cut the mating stub tenon with no noticeable gaping. After that post on woodweb I tried the same type joinery with my straight head in 1 3/4” stock. If you looked really really close you might see just a bit of heavy glue line. On 2 1/4” stock it would probably become more apparent.
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Jared, thanks for the link. Several photos there show the results in thick stock. The steeper the rake angle, the greater the resulting curve. It is worth noting that when doing rabbets with this cutter up to the mid point in height the gap will be hidden in the bottom corner of the joint.
Yes, that's what I meant by the amount of bias or deviation being greater the further away from the centre of the block you go. It's not very often that it adds up to much, but it just might depending on what you were up to. As I said above, edge gluing effectively doubles this error so my make it more visible. A few planer/jointer manufacturers made skew knife heads and this of course is dealt with easily by grinding the knives right in the machine.
If you mill two edges off to one side of the block and then try to edge glue the complimentary or opposing edge skew might cause problems much like if your jointer isn't set to a perfect 90.
Last edited by brent stanley; 02-01-2022 at 11:18 AM.
Might be worth investing in what they call a Z4 block, which is 4 cutters around the cutting circle. They are typically oriented in what they call a "dual shear" with pairs opposite each other across the block being the same, but adjacent to each other being the opposite angle. It doesn't change the mild concave cut but it can improve finish in tricky grain. The dual shear also neutralizes the very mild axial thrust produced by mono shear, though it's rarely an issue.
[OP]
Member
Thanks for all the discussion around this. I have not noticed any issues with rabbets, but honestly have not made many rabbets that are big/tall enough to suffer from a convex edge relative to the height of the cutter block itself - 50mm. I will have to look a bit closer with a square and see how much radius is actual there/visible.
Still waters run deep.
[OP]
Member
Well, so much for self control and trying to save a few (hundred) bucks. This just showed up on my steps.
4” tall x ~ 4” diameter with matching bearing. I saw several others that were more like 3x3 and that wasn’t as exciting to me I suppose. I would have gone 5” tall but I only have 5 1/2” under the nut on my T100 and with the bearing that’s pushing it.
I did happen to do some really tall 2”+ rabbets last week and measured the radius of the cut from the shear cutting knives in my rabbeting block. Wasn’t much (less than 1/64th?) of daylight top and bottom compared to the convex middle section, but less than ideal for pattern shaping to then have to flatten it back out.
I will report back on the cut quality and properties of this Schmidt Insert head and bearing setup.
Still waters run deep.
Contributor
Phillip, hope it works well for you. I know those cutters are popular now, but I think they are not as useful as corg heads . The corg. will
make a smoother straight cut and do moulding . I’m guessing that there is now a perception that they are somehow safer than corg.
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