Kickback and circle marks when using router sled with new flattening bit

[RichardWood]

Hi,

I've just purchased a flattening bit which I expect to be quite good, as it seems pretty well made and it's an expensive one (for me, at least): https://amzn.eu/d/9aDEjcN

I used it yesterday and today and I'm getting tons of kickback when I'm trying to flatten some end grain wood using a DIY router sled. I seem to be getting it even when I'm only taking off the tiniest amount, and I've taken a couple of chunks out when I took off any more (approx 2mm). I can confirm the sled and slab are flat and not rocking (significantly at least). The slab is double-sided taped down and seems stable.

i'm moving the router along pretty much under its own weight, not trying to press down on it hard or anything like that. I'm getting the issue even when taking a slight pass only a little further than the previous pass.

I've used this router sled before with a different flattening bit and also with a straight cut bit and not had any trouble, but not for a while.

My router is the Bosch POF 1400 Ace plunge router. The bit is quite wide, so I'm running it at around 1.5 on the dial, which I guess is something like 14000 RPM.

I think the impression that the router is making on the wood when it 'catches' is probably going to be telling as to what's going on, so I've attached a photo. It's strange that I'm getting a circle in the wood when it happens, because I enter the wood from the side at a constant depth, so I'm really not sure how it's happening.

Any ideas what I'm doing wrong here?

Thanks!

 

[Orraloon]

A cutterhead that size takes a bit of holding on to. On a tiny 8mm shaft even more so. Its taking a big bite and only the weight of the router holding it down so anything that can will vibrate. If there is any play on the sled or rails its gonna find it. Your pick looks like play in the sled is allowing it to dig in. You could try taking narrower passes like half the cutter head width so the waste gets cleared to the low side like plowing a field. Dial up as slow as it will go. I think the head of my thicknesser only goes at 10K. End grain is another complication. So with narrow passes, lighter cut and slower speed and feed rate dont work then the sled itself needs to be beefed up.
Regards
John

 

[johnnyb]

is this a well tried method of flattening end grain? I've no idea but end grain needs sharp rake to cut. also movement even a tiny bit can lead to problems. especially under the stress of routing. also I'm guessing the bosch is a small router max 8mm. this will also introduce issues. but it's not something I've ever done.

 

[Jacob]

Belt sander or hand plane.

 

[J-G]

... when I took off any more (approx 2mm). ...

!!! I'd consider that a massive DOC - Yesterday (on face grain [Olive]) I was taking off between 0.1 and 0.5mm at 22000 rpm with a 20mm wide fly cutter.

 

[Johnwa]

DOC?

 

[Gordon Tarling]

DOC - Depth of Cut.

G.

 

[hlvd]

Probably too much depth and direction of cut.

A sharp hand plane would be just as quick, produce less noise and be healthier for you.

 

[RichardWood]

Thanks for the replies everyone. I think the issue probably is DOC, but not my intended DOC. I reminded myself how much 2mm is and that's way more than I'm meaning to cut when I get the kickback. But the sled is wood and has been sitting in the garage for a while, and I think there is a now a little vertical movement which means that the bit is pressing in deeper than expected and making the circle marks.

I'm not sure how to solve the problem though, other than throwing the sled away and picking up a more rigid metal sled. Tbh this one was doing pretty well before so I'll be sad to throw it away!

Is my RPM reasonable?

My father in law has a belt sander that I would ideally use, but I'm on a Christmas deadline!

For the mean time, I've taken the orbital sander to it after getting the most part done with the sled, and it's come out pretty nicely. So I'll leave figuring out this to the new year!

Thanks

 

[RichardWood]

As for a hand sander, I do have one (I think the cheapest possible from Screwfix) and it's terrible and extremely blunt. One of these days I'll sharpen it and figure out how to use it without taking absolute chunks out left and right!

Edit: I mean hand plane! In response to hlvd's suggestion

 

[__jvc26]

I imagine you mean a hand planer? As a sander doesn’t require sharpening only fresh abrasive.

 

[RichardWood]

I imagine you mean a hand planer? As a sander doesn’t require sharpening only fresh abrasive.

Whoops yeah sorry it was a response to hlvd's suggestion to use a hand plane!

 

[Spectric]

For such a cutter I would not have looked at anything less than a 1/2 shank and then only taken light cuts. I use this one from Wealdon Surface Trim but it does not have replacable cutters.

 

[baldkev]

Ive got a chunky 50mm trend flat bottom cutter in 1/2". I run it on a hitachi m12 ( 2kw i think ) and it'll do 4mm at half cutter width quite well, but its a heavy duty setup and i hang on tight / keep a bit of downwards pressure.
Rather than binning your sled, set it to take off half a mm to 1 mm and just aim to nibble away 10mm wide per pass.
As spectric said, ideally a 1/2" router would be used, but as long as you arent overloading the router and bit, it should cope

 

[sams93]

Thanks for the replies everyone. I think the issue probably is DOC, but not my intended DOC. I reminded myself how much 2mm is and that's way more than I'm meaning to cut when I get the kickback. But the sled is wood and has been sitting in the garage for a while, and I think there is a now a little vertical movement which means that the bit is pressing in deeper than expected and making the circle marks.

I'm not sure how to solve the problem though, other than throwing the sled away and picking up a more rigid metal sled. Tbh this one was doing pretty well before so I'll be sad to throw it away!

Is my RPM reasonable?

My father in law has a belt sander that I would ideally use, but I'm on a Christmas deadline!

For the mean time, I've taken the orbital sander to it after getting the most part done with the sled, and it's come out pretty nicely. So I'll leave figuring out this to the new year!

Thanks

Do you have photos of the sled?

 

[no idea]

Is this simply the wrong tool for the job? End grain with a large cutter with insufficient power behind it? Try using a conventional bit and see if the issue is still there. I suspect the end grain is causing the large cutting edges to catch and dig in.