Insert Tooling Versus Knives

      Machine owners weigh the pros and cons of standard planer knives compared to helical insert tooling. It gets complicated. October 27, 2013

Question (WOODWEB Member) :
Does anyone have a current model SCM S630 (24 inch) planer? Iím trying to decide between the Tersa and helical type head. My use would be relatively low volume - red oak, mahogany, and occasional maple, studio furniture type creations. The dilemma is that I know I'd be perfectly satisfied with the Tersa head, but due to circumstance I won't go into here, I could get an S630 with helical head for the same price! Iím thinking since helical is probably more popular and normally $3,100 more expensive it might be better from future re-sale standpoint to go with helical head.

On that particular planer and helical head can you achieve results without lines and fuzz if the 200 plus carbide inserts are sharp, or is the Tersa head always going to give more impressive results from a slick finish standpoint?

Forum Responses
(Solid Wood Machining Forum)
From contributor E:
If you can get the SCMI with the helical carbide insert head for the same price, don't even think about it. Jump all over it. The issue about the inserts leaving witness lines is so overblown I can't believe it. Everyone I know always sands their parts after they come out of the planer anyway, so whatís the issue? The longer life of the knives, reduced tearout, and reduced noise trumps everything else in my opinion. I speak from experience as I had one in an SAC planer.

From the original questioner:
"I speak from experience as I had one in an SAC planer." Was it a Tersa or Helical carbide insert?

From contributor E:
I had the helical carbide insert.

From contributor F:
In your particular case you may be best served by the insert head. This is a topic that comes up frequently and if you search the Knowledge Base you'll find plenty of info. The inserts leave a nice finish and will last a long time before having to rotate. The problems, while minor, usually come when you have to rotate or replace them. However, since youíre talking about moderate to light use you may never need to replace them. For what itís worth I had a 20" planer with the inserts in the past and now run a 20" SCM with a four knife head and grinder. I personally would never go back to the inserts.

From the original questioner:
"In your particular case you may be best served by the insert head." Right, but the discussion usually concerns the Byrd Shelix head and I suspect there may be some minor differences in the SCMI version of that head, thus the mention of the specific SCMI planer.

"FWIW I had a 20" planer with the inserts in the past and now run a 20" SCM with a four knife head and grinder. I personally would never go back to the inserts." Yikes, talk about mixed messages!

From contributor F:
Sorry if it seems like a mixed message. The point being that the insert heads are (in my opinion) not much better than anything else and to me there's no debate left. They have advantages and disadvantages and as such we all have our opinions. There are many guys here that went with other options, such as the Tersa.

So basically you have to weigh the pros and cons and decide for yourself. My decision serves me well, but may not be the best for you. You may get a response from someone that happens to have that specific planer, and that specific head, and also happens to visit this forum. I just figured while youíre waiting we may be able to help a little. I'm not familiar with that specific head, but the head I used was not a Byrd, but worked every bit as well.

If youíre concerned the finish from the SCM will be different from the other insert heads, maybe you can have the current owner/dealer plane a piece of wood and send it to you. For what those machines run it seems a small thing to ask, and you would be able to judge the finish quality for yourself.

From contributor E:
I'm pretty sure that Byrd makes those heads for SCMI so you are dealing with a Shelix head. That's what I had in my SAC planer. Different strokes for different folks, but I used to grind my knives in the head just as Contributor F does when I had a Powermatic model 180 years ago, and I would never go back to that.

Contributor F - for what itís worth I've followed your posts on this subject since youíve picked up your new planer and I can't help but think you had a knock-off of one of those heads in your old Bridgewood planer. Even if was a 20" planer they weren't putting 125 mm diameter heads in those. It was more like 75-85 mm. That may be part of the reason you weren't happy with it. The diameter of the head is also important in these things. On the smaller machines they're running small diameter heads in those, and I suspect that has a lot to do with less than optimal cutting.

From the original questioner:
"I'm pretty sure that Byrd makes those heads for SCMI. So you are dealing with a Shelix head." I called Byrd and asked and all that I found out is that they did ship them to SCMI distributors sometimes. I think this one came straight from Italy with the helical head so I don't know what to think. Is the name "Byrd" stamped on the head somewhere visible?

From the original questioner:
Forgot to mention that I did get confirmation the SCMI insert is the same 15mm square x 2.5mm thick as Byrd inserts. Now I worry that the darn mount hole or the edge taper might be different! Maybe I worry too much, however I'm more from the machine tool world where sometimes manufacturers do pull little tricks where a part seems the same as standard, but has the slightest difference that makes you beholding to them for the replacement.

From contributor F:
To contributor E: You have a good memory! It actually was an import and it was a smaller head than the SCM. However one thing I never had a problem with was the quality of cut. The import knock-off head cut as clean as you could want through the gnarly material I sent through it. I had other issues with the machines performance, just not with the quality of cut.

I don't want to come off as knocking the insert heads if that's what it sounds like? There are a lot of guys out there very happy with them. I'm just saying for me personally when I weigh the pros and cons, I like the advantages my straight knife planer offers and won't be going back to an insert head.

From contributor O:
You asked about Tersa and Iíve had these on a jointer, planer, and S4S machine for ten years. We are a two-three man shop producing doors and windows. Carbide Tersa will give a slick bright finish for a long time. M42 is good at first but will lose it pretty quick. M 42 Tersa is disappointing for wear unless you are only planing clear softwoods. I have come to the conclusion carbide is the most economically grade of Tersa for our operation. The S4S machine will go for two years between sharpening with the carbide. We only run two knives in our heads instead of four. We have found the quality of cut is almost the same as four except in the jointer.

With no experience on insert spiral planers I don't know what the best choice is. I have an Oertili spiral shaper head we use for curve shaping and like it a lot. I agree the small wittiness lines are not a problem. I think spiral insert may be quieter, but Tersa is not bad for noise. Tersa Is a lot faster to change and the carbide can be re-sharpened. If I am running junk wood I can pull the knives quickly and put some beaters in. By the same token an entire Tersa knife could be ruined by hitting metal vs. just ruining a couple inserts.

Quality of cut may be a little better on difficult woods with the spiral. I have not had any issues with cut quality with Tersa either. Last time I looked, two Tersa knives for my 24" planer cost about $400. In the end it costs a lot to mill wood whatever system you choose. I agree with Contributor E - after 18 years of straight knife planers I would never go back to that, for the noise alone.

From contributor E:
The cost on a 24" is around $300 if memory serves me correct. I'm now running a 24" spiral top and bottom planer with 30 x 12 x 2.5 mm double sided inserts and they were a little over $3 each in quantities of 300, so the cost for me is double. It's a six row spiral so just under 100 knives per head. I got a year out of those knives which equates to about 60,000 feet of lumber through the machine.

I do agree that if you're running a Tersa head, carbide is the most economical route over the long haul. Good to hear you found a grinding service that can re-sharpen them for you. You're right that no matter what system you're using it costs money to mill lumber, whether it's time grinding the knives in the head, or the cost of the inserts themselves. I'm going through a whole knife change this weekend, so I'll be a couple of hundred inserts lighter.

From the original questioner:
There are four sharp corners per insert, so assuming no major damage to insert that would make the helical carbide head less expensive than the Tersa overall. Of course the Tersa is much faster to change out the entire head to new edges. Loosening 252 screws and turning 252 inserts and scraping off any residue and making sure each seat is clean is not a task I look forward to! Maybe I need to figure in the cost of a temp worker for that!

From contributor O:
You work a lot faster than I do. We only go through about 30-40K board feet per year. Itís hard to compare the planer to the S4S for knife wear. We get four edges on the S4S machine with two edge knives by flipping end to end on the 10Ē horizontal and 6Ē vertical heads. Every board foot goes through twice though, once to S2S and again to S4S the laminated scantling. We don't use our planer much and still have a stock of M42 we are using up. When I change that to carbide it should go a long time.

From contributor E:
I suspect our costs are pretty much the same for tooling. I'm sure the grade of carbide Tersa is using is pretty good stuff. As I look back on the last yearsí worth of lumber consumption 60,000 might be a little high. It was probably more in the 40,000 range. Like you it is still two passes before hitting the target thickness but that's still a lot of lumber. Good to hear you're busy if you're putting that much lumber through the system.

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