Tenon cutter not cutting square

[Albert Lee]

what am I not doing right? I lost about 1mm when I measured it.

The tenon cutter is Omas K408

Was I too quick in moving the carriage?

here is the video link


https://www.youtube.com/watch?v=wIEsrN15pk8

the hood was removed to show what was going on.

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[Stanea Laurentiu]

Mount a sawblade onto the spindle, place a magnetic dial indicator onto the sawblade and check if the spindle is perpendicular to the shaper table.

[Joe Calhoon]

Not going too fast Albert. Have you checked the travel height of the sliding table in relation to the shaper cast top? Using a dial indicator or feeler gauge to measure height of table from one end of stroke to other.
Is shaft square to the sliding table? Check this by clamping a straight edge between the spindle spacers checking with feeler gauge out 500 mm or so on the sliding table.

[Michael Todrin]

For diagnosis purposes check both of the shoulders for square relative to the tenon and to the stock. Maybe only 1 cutter is off. Also, maybe check the resulting tenon without pulling the stock back through the cutter.

[Lee Schierer]

Ordinarily you don't want to pull a piece back through a moving cutter. Try making a tenon without coming back through the cutter.

[Warren Lake]

looks like a new machine so would hope it came square to the table. Put a dial magnetic base or other way on the spindle and do a rotation see what the dials says to be sure its square to the table

what speed is the cutter head rated for
what speed are you running
feed rate looks a bit slow, or at least put a backer there as you slowed down more for less break out

dont pull back across the cutter head its already been machined
your blank is two laminations it should be one or three

[Rich Engelhardt]

https://www.scosarg.com/omas-adjustable-groover-d-40-d-140-z-4-v-4-b-31-57

Is this what you have?

[Albert Lee]

https://www.scosarg.com/omas-adjustable-groover-d-40-d-140-z-4-v-4-b-31-57

Is this what you have?

Almost, this is the one I have.
https://www.scosarg.com/omas-adjustable-groover-d-30-d-250-z4-v4-b-12-5-22
D is 250.

[Albert Lee]

Not going too fast Albert. Have you checked the travel height of the sliding table in relation to the shaper cast top? Using a dial indicator or feeler gauge to measure height of table from one end of stroke to other.
Is shaft square to the sliding table? Check this by clamping a straight edge between the spindle spacers checking with feeler gauge out 500 mm or so on the sliding table.

Thanks Joe, I will be doing that. looks like I will be doing a bit of checking today..

it appears the bottom cutter block is cutting concave, the top block is cutting ok if I move slowly.

The tenon in this video is actually one of the best result. others I am getting -2mm differences.

[Joe Calhoon]

Albert,
If I’m understanding right the tenon thickness varies from the shoulder to the tenon end? Or does it vary from one side of board to the other?

Looking at your bottom cutter I think it is Ok but check to see if the insert cutters are seated correctly and slightly below the knickers. I have seen these get off from the factory and that can cause problems. If the sliding table is solid without play it’s no problem to draw the piece back through the cutter. If there is play though this will cause a problem. A lot of in table sliding shapers have this problem but usually the side mounts are sturdy.

Here is how I check side mount sliding tables. See if the sliding table is square to the shaft. You can do the same thing with the cast top.
501131 501132
Check the travel of the sliding table to make sure it is not running uphill or down hill. This can also be done with feeler gauges if no dial indicator.
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[Kevin Jenness]

It appears the tenon is tapered from the root out to the tip. I have seen this result from a tenoner with separate tenoning heads and inaccurately set knives, but I can't visualize how that can happen with two cutters on one vertical shaft unless the table is tipping on the return stroke. I would do the table travel test shown in Joe's second pair of photos and put some up/down torque on the end of the table while looking for variations at the indicator. It seems odd that you would have a problem there on a new heavy sliding table unless there is something loose. Have you tried checking the tenon dimensions without pulling the workpiece back through the cutters?

The feed rate in the video seems quite slow to me.

[Warren Lake]

Its cutting on the back stroke. there are also different results as albert said that is the best one. I never questioned why they taught us not to pull back and should have. Most people do it. Maybe pushing down on the forward stroke and lifting up pulling it back but there should be no play in that set up. Guys cut tennons on a chunk of plywood with a destatco clamps.

[Jared Sankovich]

It appears the tenon is tapered from the root out to the tip. I have seen this result from a tenoner with separate tenoning heads and inaccurately set knives, but I can't visualize how that can happen with two cutters on one vertical shaft unless the table is tipping on the return stroke.

I'm with you on the "I can't understand how you can cut a tapered tenon on a stacked vertical spindle"

Unless like you say the table has vertical play or can rock.

[Albert Lee]

Albert,
If I’m understanding right the tenon thickness varies from the shoulder to the tenon end? Or does it vary from one side of board to the other?

Looking at your bottom cutter I think it is Ok but check to see if the insert cutters are seated correctly and slightly below the knickers. I have seen these get off from the factory and that can cause problems. If the sliding table is solid without play it’s no problem to draw the piece back through the cutter. If there is play though this will cause a problem. A lot of in table sliding shapers have this problem but usually the side mounts are sturdy.

Here is how I check side mount sliding tables. See if the sliding table is square to the shaft. You can do the same thing with the cast top.
501131 501132
Check the travel of the sliding table to make sure it is not running uphill or down hill. This can also be done with feeler gauges if no dial indicator.
501133 501134

Joe I will do this check but what I want to know is, the tenon cutter is cutting tapper. why is that? if the sliding table is out of square, ok, I will cut trapezoid, but I am not cutting trapezoid, I am cutting a taper on both top and bottom plate.

[Albert Lee]

It appears the tenon is tapered from the root out to the tip. I have seen this result from a tenoner with separate tenoning heads and inaccurately set knives, but I can't visualize how that can happen with two cutters on one vertical shaft unless the table is tipping on the return stroke. I would do the table travel test shown in Joe's second pair of photos and put some up/down torque on the end of the table while looking for variations at the indicator. It seems odd that you would have a problem there on a new heavy sliding table unless there is something loose. Have you tried checking the tenon dimensions without pulling the workpiece back through the cutters?

The feed rate in the video seems quite slow to me.

My thought too, I can't visualise or think of a reason why it is cutting tapered, and yes you are correct, its tapered from root out to the tip.

looks like another interesting issue that can to be documented...

[brent stanley]

Might be diagnostic in some capacity to try each block independently and make an offset tenon (one cheek/shoulder) with them to see what the measurements are. Use each of them over and under the stock.

[William Hodge]

Try running a rail into the shaper to the point where the tenon cutters are top dead center, then back out. See if it's tapered. Then put [pencil lines on the work piece, and run tit through . Look to see if and where the pencil lines are being cut off.

On a tenoner, I run one head at a time when truing up the copes and tenon heads. The other side is not cut. If there's taper, I can tell by measuring the thickness from the un cut face to the cut face. On a shaper, I would pull the top cutter off, and see if the bottom cutter is running weird. Then try just the top cutter.

I get the bottom cope head parallel to the table by tilting the table to match the cope head.

[Warren Lake]

I cant visualize how that is possible other than if there were two cutter heads cutting 90 degrees to make the tennon like in a tennon machine. Have you called the tooling company and id also call the shaper company if its an SCM sliding gizmo then id be asking. Both of them should have many years experience at least if older people working there. The fact that you are getting different results means something is moving or loose or has play in it. there is some issue with movement there.

Id prefer a digital caliper that reads to .0005. take test pieces and go through one time cut and label the measures in the four critical places with a fine sharpie. Once labelled id pull them back and see what changes you get.

[Paul Haus]

I've watched the video multiple times and to me it appears that the sliding jig raises and lowers as the piece is passing through the cutter. Hard to confirm suspicions without actually seeing it in operation though. All I can suggest is some possibles, so take it with a grain of salt. Confirm the spindle is perpendicular to the table and there is no vertical play in the spindle. Check each of the cutters (with power disconnected) with a dial indicator to insure they are true. Check the sliding table to insure whether it's raising and lowering while cutting as it appears to be happening in the video.
That's where I'd start and go from there.

[Aaron Inami]

This is a really hard problem. I took a screen shot of the material just before Albert pulled it back through the cutters. It looks like the tenon is already tapered at this point. The only thing I can come up with is incorrectly installed cutter knives.
501244

It's a very long piece of material. It might be possible that the sliding jig is tilting the material down and then up at some point during the movement.

[Aaron Inami]

After some thought, I think the cutters are just fine and square. I think the piece is tilting down or up as it's being moved through the cutter. One of two things could be happening here:

1. It is a very long board that needs to be supported at a perfect 90 degree to the cutter. If your clamp/jig in the only thing that is supporting the board, the weight of the board could be pulling it down when it passes off the table (or something similar is happening as weight of the board or weight of the clamp/jig moves towards the back of the machine).

2. The sliding table could have a twist in the slider alignment which could cause the sliding table to tilt up/down as the material is being run through the cut. I don't know if you can do alignment on the slider or if it's non-adjustable. I would put a straight edge on the sliding table and then move the slider back and forth to see if the end of the slider is tilting up or down during movement.


One thing you could do to verify the cutter is by doing a tenon cut operation using a smaller piece of material and running from right-to-left on the front table. That should prove the cutter is not the problem.

[brent stanley]

One other quick check that could offer diagnostic information is the comparison of the tenon thickness to actual tenon disk spacing. If the greatest tenon thickness (at the shoulder) is less than the spacing of the discs then that would be another nugget of information.

[Joe Calhoon]

Joe I will do this check but what I want to know is, the tenon cutter is cutting tapper. why is that? if the sliding table is out of square, ok, I will cut trapezoid, but I am not cutting trapezoid, I am cutting a taper on both top and bottom plate.

Very strange for sure Albert. Did you ever figure anything out? Your material looks like fast growth pine? Is it dry? I have seen tenon thickness vary when using Red Grandis scantlings for our window building workshops. It’s a sketchy material with a mind of its own but the variation is nowhere near what you are getting!

[Jared Sankovich]

Watching again it looks like its burning mid cut, then cleans up as the knife passes again.
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[Mel Fulks]

Ordinarily you don't want to pull a piece back through a moving cutter. Try making a tenon without coming back through the cutter.
Yep , and go a little faster . I can tell you are your own boss ‘cuz you ain’t been fired ! The wood moves as it’s being cut.

[brent stanley]

Watching again it looks like its burning mid cut, then cleans up as the knife passes again.
501354

I saw that too, but it looks like an artifact of the camera to me....shutter trying to resolve looking through the gap in the spinning discs. When he pauses at the end before pulling back, it's not there.

[Jared Sankovich]

I saw that too, but it looks like an artifact of the camera to me....shutter trying to resolve looking through the gap in the spinning discs. When he pauses at the end before pulling back, it's not there.

If you watch at reduced speed It's cleaning up the burn as it passes the knife tje second time on the back of the cutting circle.

Knife set to low, discs flexing or table flexing all seem like possibilities.

501356

Something in here is rubbing and burning. If it's rubbing it's deflecting the discs apart and likely the reason for the taper.
501357

[brent stanley]

If you watch at reduced speed It's cleaning up the burn as it passes the knife tje second time on the back of the cutting circle.

Knife set to low, discs flexing or table flexing all seem like possibilities.

501356

Something in here is rubbing and burning. If it's rubbing it's deflecting the discs apart and likely the reason for the taper.
501357

I misunderstood you, I thought by "passes again" you meant the back stroke. That could be a tenon too long for the discs (the boss there could be rubbing) or the discs aren't inverted, can't get a shot of the orientation. Typically adjustable groovers (which is what this set is, not true tenon discs) when used for tenoning need to be inverted from groovers orientation. I believe these were installed inverted, can't really see, my subscription expired so I cant see the posted pictures above.

[Joe Calhoon]

Brent they are set correctly for tenoning. You can tell by the position of the knickers. Yes, true tenon disks are better as the adj groovers sometimes are depth limited for this operation. But if he was hitting the raised part of the disk the wood would be burned. Also if the knives are set higher than the knickers you would see burning on the top knife edge. I don’t see that but hard to tell from the pictures.
the video is shaky so had to really see what is happening.
Tough to armchair quarterback without hearing back from Albert.

[brent stanley]

Brent they are set correctly for tenoning. You can tell by the position of the knickers. Yes, true tenon disks are better as the adj groovers sometimes are depth limited for this operation. But if he was hitting the raised part of the disk the wood would be burned. Also if the knives are set higher than the knickers you would see burning on the top knife edge. I don’t see that but hard to tell from the pictures.
the video is shaky so had to really see what is happening.
Tough to armchair quarterback without hearing back from Albert.

I expect there would be a lot of back pressure too and doubtful the burning from that would get cleaned up . I need to get my subscription renewed so I can see pics again!

[Albert Lee]

***UPDATE***

I have resolved this issue today!

for a while I thought I had an issue with my OMAS cutter block, even took it to a machinist to check, the machinist commented maybe it is the sliding table?

I was getting the same issue with another cutter block recently, so I wondered if it was something else, maybe my setup? maybe the sliding table?

I had to do 100 x tenon cut recently. so I finally investigated this today and played around with the spindle moulder.

I know it will create burn mark past mid point, I thought to myself. MAYBE, just MAYBE, the tilt of the spindle is not dead on 90 deg. although it is reading "0" on the screen?

I started with + and - 0.1 degrees on the spindle. no improvement, then + 0.2 deg. slight improvement!!
I cranked it up to + 1 deg. it was creating burnt marks on the other side, so I adjusted back to + 0.9 deg... and EUREKA!!!!

Below is the video I took today. no more burn marks and the cut was square!


https://www.youtube.com/shorts/uespGfV0l7M

a few months ago I did move the machine and the move could have affected the calibration? the tilt was showing a funny number after the move and I thought I zero'ed it but it seems I didnt zero it properly.

[Kevin Jenness]

Good that you cured the issue. I am surprised that you did not tram the spindle to start with, and that it fixed the problem. I thought that the tenon thickness was different at the root and end, but perhaps I misunderstood and the "taper" was a constant thickness tenon out of plane with the workpiece face. I suspect any burning is due to the slow feed rate.

Can you adjust the spindle exactly square to the table manually using a straightedge and taper gauge or feeler gauges and then zero out the display? 0.1 degrees seems rather a coarse interval for calibration (or can you make electronic adjustments in smaller increments?).

[Aaron Inami]

Theory: the floor flatness on the old location may not be the same for the new location. They may have created a twist or un-twist on the main table of the machine and caused the spindle angle to deviate that .9 degree. In any case, it's great that you've solved the problem. You might want to think about adding leveling feet and making sure the table top and perfectly level so that there is no twist. This can affect the accuracy of the sliding table as well.

[Wes Grass]

Not familiar with the shaper you have, but looking at the table insert and the way it's extended on one side, looks to me the spindle tilts in that direction. If so, your sliding table is 90° out from where it should be installed. So you get this, which *should* taper it the opposite way, but maybe something is rubbing.

**** Duh, I had the measurements backwards, it IS thinner at the end ****

Sheesh ...

506800
Vs:

506801

If not, well ... like I said ... not familiar ...

[Kevin Jenness]

I suspect Wes has grasped the essential point, that the spindle's rotational axis is at 90 degrees to the travel of the sliding table. It makes sense that it would tilt toward the front of the table for standard edge milling rather than toward the side on which the table is mounted. In that case the slider is meant only for tenons parallel with the table and any forward tilt of the spindle would in fact produce a tapered tenon and even burning if the tilt is sufficient to negate the clearance designed into the cutters.

[Jim Becker]

Cast iron and steel bend/flex. It might be a very small amount, but a different floor can absolutely "move the mark" and cause that little bit of "out" that you describe. Hopefully, you can correct the setup to dead-nuts on in the new location now that you know it's off a proverbial hair.

If I move my Stubby 750 lathe, I have to carefully check things to insure that the center's line up and make adjustments/shim to fix if it's out. That's 800+ lbs of cast iron on a steel base and yes, the floor matters.

[Warren Lake]

Hard to believe a serious shaper with a plate steel base then thick top would flex. Be good to know ive wondered about my saw which is 1,300 lbs and cant tell if it can flex The top of rhe shapers is likely heavier than the saw. Question for SCM

[Wes Grass]

Hard to believe a serious shaper with a plate steel base then thick top would flex. Be good to know ive wondered about my saw which is 1,300 lbs and cant tell if it can flex The top of rhe shapers is likely heavier than the saw. Question for SCM

An 8500 lb cast iron machining center will twist itself out of square if the slab settles under it. Been there. My lathe, roughly the same weight, has 6 pads to dial in twist, and sag, of the bed.

As *someone* once said: 'Everything is made of rubber'.

My little lathe needs one of the pads just barely past touching to be straight. It either warped as it aged, or sat for awhile out of level. Cast iron also 'creeps'.

[Warren Lake]

ill still ask SCM sometime all bases of machines are not the same, tops as well. I had no flexing when lifting and trying to level my table saw, it was annoying to shim it, would have been easier if it did flex. Then add in cast iron sag over time and other like wear from a power feed and more dynamics. Id want to hear it from SCM on that particular machine if and how much it could move.

[Albert Lee]

did a quick check last night, the back of the machine is lower than the front by 2mm over 1000mm. this may have caused the issue. I am going to level the machine today and see if this improves things.

[Albert Lee]

ok this is what I did today.

I levelled the machine first - this was never done after I moved the machine - I assumed the concrete floor was level but it was out by 2-3mm, back being lower.

after levelling I did a test cut - still need that +0.9 deg to cut properly.

I then went through machine's technical setting, there are probably hundreds VERY technical parameters such as rotational speed, acceleration, angular rotation, deceleration time...etc, I dont think touching any of these is a good idea.

on one of the sub window there is a calibration tap. thought I give it a try - machine started calibrating itself. once the calibration is completed, I gave it a test cut. and its PERFECT. even better than my manual "+ 0.9 deg" setting.


506908

[Jim Becker]

No harm in leveling it even if it alone didn't clear the issue! And it's good that the calibration thing did the job. I have a suspicion that leveling the machine didn't hurt that either.

[Warren Lake]

throw it out of level on purpose and see what it does. Its not level anyway it could be sitting supported on four corners equally and have a tilt. I dont have time to try pulling a support out of one corner now so it floats and see what that does. Get the feeling it would be nothing.