slab flattening sled

[Justin Rapp]

I am going to make a sled to flatten slabs plan to use linear rails (SBR series)

There are SBR12, 16 and 20 (in mm's) and wondering if anyone has built a sled with these rails and what size did you go with.

here is an example of a set that is 20mm (SBR20)

https://www.amazon.com/gp/product/B088YWJPKT/ref=crt_ewc_title_dp_3?ie=UTF8&psc=1&smid=A27FLKY64E6N9J

Thanks in advance

[Jamie Buxton]

I'm confused. In the usual router bridge slab flattening jig, there are fixed rails which are parallel to the sides of the slab, and there are moving rails which run cross-grain, which the router rides on. Which of those are you talking about?

[John TenEyck]

If you are making a power driven sled those should work well. If you are making a manual sled they are a waste of money IMO. Wooden rails work just fine. And you don't need any rails at all if you have a flat bench/table for a base.

https://lh3.googleusercontent.com/pw/AM-JKLX4qKfr6bGoA0qdjMyXXWsUWa_ayeaVB2WZBBZBkFDmNMYK3 3BC_zzuPjnTFI37WBYHfgI98_HuSMNHMcfivcaztwqlJqdJmXo oZ5YFQbs4wdLV-RCNwB8mLKD8zu8F1JksXjWgRlkwu4f8DqvO-DZ23w=w820-h615-no?authuser=0

John

[Joe Rogers]

I used a set of twin bed frame rails. Width set to match the router base. End rails can be adjusted for height.
Joe

[Justin Rapp]

I'm confused. In the usual router bridge slab flattening jig, there are fixed rails which are parallel to the sides of the slab, and there are moving rails which run cross-grain, which the router rides on. Which of those are you talking about?

It's two pair, one longer pair that go on either side of the slab. The second pair holds the router and rides perpendicular on the first set of rails. The end result is much like Woodpecker's sled.

[Jim Becker]

If you decide to go this route, I'd definitely use the heavier 20mm diameter product for durability. The concern I have is that the longest length is "only" 2000mm (about 78") so that's going to be limiting if you intend to mill longer slabs without repositioning them...something that can be "fun" while trying to maintain registration.

[Bryan Lisowski]

I would look at the slab flattening sled that Lee Valley sells. If you didn’t want to buy, there design seems to be good and probably easy to duplicate the router holder, cause the rails are pipe you supply.

[Justin Rapp]

If you decide to go this route, I'd definitely use the heavier 20mm diameter product for durability. The concern I have is that the longest length is "only" 2000mm (about 78") so that's going to be limiting if you intend to mill longer slabs without repositioning them...something that can be "fun" while trying to maintain registration.

The rails are designed to extend by adding another length, just like railroad tracks.

[Jim Becker]

The rails are designed to extend by adding another length, just like railroad tracks.
True. I overlooked that. My bad.

[Jamie Buxton]

My flattening rig is all-wood, and manually operated. One issue is that the cross-grain rails can flex under the weight of the router and my hand pressure. Flexing and bouncing leaves divots in the workpiece surface. So my rails are 5" tall hardwood. If you use the linked rails - particularly the small-diameter ones - as the sole supports for your router, I think they'll flex. You can fix that with wood rails, so the wood supports the weight, and the linear bearing is the running surface for the router.

[Dan Gaylin]

I made mine with a set of linear guide rails bought on eBay. Not very expensive and very smooth.

[Justin Rapp]

My flattening rig is all-wood, and manually operated. One issue is that the cross-grain rails can flex under the weight of the router and my hand pressure. Flexing and bouncing leaves divots in the workpiece surface. So my rails are 5" tall hardwood. If you use the linked rails - particularly the small-diameter ones - as the sole supports for your router, I think they'll flex. You can fix that with wood rails, so the wood supports the weight, and the linear bearing is the running surface for the router.

Well i'll definitely go with the 20mm so the rails are stronger. I don't think they will flex under the weight of a router. These thing are used for larger machine heads that are much heavier than a router. My concern is if my porter cable 1 3/4 hp will be able to swing the 2" flattening bit. I have a 3 1/4 in my router table which was a motor only purchase, not a plunge.

[Justin Rapp]

I made mine with a set of linear guide rails bought on eBay. Not very expensive and very smooth.

Which ones did you go with?

[Shawn Hinsey]

I used 80/20 series 10 extrusions with the linear bearings mounted on top for the longer run and below for the cross piece. I used it on a slab that was ~4’x11’. You could expand the basic idea to any size really.

[Kevin Jenness]

My concern is if my porter cable 1 3/4 hp will be able to swing the 2" flattening bit.

That is a large bit so you will need to observe the max rpms (probably around 15,000) and take light cuts. I have a PC 7518 motor in my cnc router and run a 2 1/4" spoilboard bit, typically removing .020" at 250-300 in./min on ultralight mdf. That is a comfortable rate on my machine - with a deeper cut the rpms slow down. I would recommend a smaller diameter bit as well as a more powerful router for what you are doing as you will want to knock down the high spots quickly and that will be a pain with the depth of cut you will be limited to. When you run a large bit into a high spot it can be an unwelcome surprise. With a 1 1/4" bit you will be able to flatten a good percentage of a typical piece with your first pass at a greater depth of cut.

I have done a bit of slab flattening by hand and it is quite tedious and dusty. If you can rig up some dust collection it would be a good thing. If you have a regular need for it you may want to invest in cnc or sub it out.

[Jim Becker]

On the router question, for this kind of work, you generally will be better served by a beefier router motor so you can both swing the larger tooling as well as not over-stress the tool doing it. This can sometimes be hard work and it also makes for long run times. I'd say minimum the heavier 12 amp router but preferably the "big one" in whatever flavor is most cost effective for you for this particular application.

[Erik Loza]

To the OP, not sure if this got mentioned already but if this is just a once-in-a-while thing, I would look into subbing it out. Any big millshop could flatten and sand your slabs pretty easily. Just a thought.

Erik

[Dan Gaylin]

It was some time ago so I don't remember the exact model/seller. The ones I used are very sturdy, steel rods about 1" diameter. Around 60" long.

[Justin Rapp]

To the OP, not sure if this got mentioned already but if this is just a once-in-a-while thing, I would look into subbing it out. Any big millshop could flatten and sand your slabs pretty easily. Just a thought.

Erik

I have a supplier that has a mill and he can flatten for me. I'd suspect he'd even let me just use his sled, and it's got a 3.25 triton on it so the power is there. While this is a once in a while activity for me, I also want it for end-grain cutting boards and larger glue-ups that are bigger than my 13" planer can handle. And on top of that, this is a hobby for me, so it's all about doing the work.

[Justin Rapp]

That is a large bit so you will need to observe the max rpms (probably around 15,000) and take light cuts. I have a PC 7518 motor in my cnc router and run a 2 1/4" spoilboard bit, typically removing .020" at 250-300 in./min on ultralight mdf. That is a comfortable rate on my machine - with a deeper cut the rpms slow down. I would recommend a smaller diameter bit as well as a more powerful router for what you are doing as you will want to knock down the high spots quickly and that will be a pain with the depth of cut you will be limited to. When you run a large bit into a high spot it can be an unwelcome surprise. With a 1 1/4" bit you will be able to flatten a good percentage of a typical piece with your first pass at a greater depth of cut.

I have done a bit of slab flattening by hand and it is quite tedious and dusty. If you can rig up some dust collection it would be a good thing. If you have a regular need for it you may want to invest in cnc or sub it out.

A 1 1/4 bit might be the way to go until I burn out my PC and forced to buy a new one :) Dust collection isn't an issue, I have a 3hp cyclone. I plan to build the sled with a dustport. Similar to the woodpecker pro. Like what John did in the picture he posted above.

[Jim Becker]

Justin, I use a 1.25" tool for spoilboard maintenance and flattening on my CNC machine with a 1.7kw spindle. (about the equivalent of a 2.25 hp motor) While the bite is smaller, it does a great job. No worries using the smaller tooling as it only takes a little more time. And yea, get a solution for dust/chip collection on that fixture...these things make a BIG mess!

BTW, I use an Amana insert tool for this long wear but a fresh edge when you need it for "that special piece".

[Erik Loza]

...this is a hobby for me, so it's all about doing the work.

Gotcha'. Just spitballing but what about a 16" planer? Would that solve it or still need wider?

Erik

[Justin Rapp]

Justin, I use a 1.25" tool for spoilboard maintenance and flattening on my CNC machine with a 1.7kw spindle. (about the equivalent of a 2.25 hp motor) While the bite is smaller, it does a great job. No worries using the smaller tooling as it only takes a little more time. And yea, get a solution for dust/chip collection on that fixture...these things make a BIG mess!

BTW, I use an Amana insert tool for this long wear but a fresh edge when you need it for "that special piece".

I was looking at the whiteside 2" spoiler bit, and would take smaller cuts, as i am thinking of an upgraded router if I use it enough. I also found CMT has a nice one with replacement blades, they have both 2" and 1 1/2. Might be worthwhile as i'd get 4 sides replacing them and they are about 15 bux for a set of 3.

[Justin Rapp]

Gotcha'. Just spitballing but what about a 16" planer? Would that solve it or still need wider?

Erik

A 16" planer would be great, but not wide enough for the project that is ahead of me as the top is 24" wide. And future end-grain cutting boards are in the plan also.

I also have a pile of cookies made from Ash that i will need to flatten once dry for some artwork my daughter is going to do.

[Jim Becker]

I was looking at the whiteside 2" spoiler bit, and would take smaller cuts, as i am thinking of an upgraded router if I use it enough. I also found CMT has a nice one with replacement blades, they have both 2" and 1 1/2. Might be worthwhile as i'd get 4 sides replacing them and they are about 15 bux for a set of 3.
I really like insert tooling for this kind of application because you get those edge changes. Like I mentioned, I use Amana, but there are other options as you note.

[Justin Rapp]

I really like insert tooling for this kind of application because you get those edge changes. Like I mentioned, I use Amana, but there are other options as you note.

Ouch that is an expensive bit. $200...

[Jim Becker]

Ouch that is an expensive bit. $200...

Yes, up front cost is higher for insert tooling...but over time, since you're only replacing the small knives after you've used all four edges, the cost is less. Meantime, you have nice sharp tooling. I do understand the "pain", however, at the beginning....I also bought the insert versions of their vee-bits. :) But they do cut crisp!

[Justin Rapp]

Yes, up front cost is higher for insert tooling...but over time, since you're only replacing the small knives after you've used all four edges, the cost is less. Meantime, you have nice sharp tooling. I do understand the "pain", however, at the beginning....I also bought the insert versions of their vee-bits. :) But they do cut crisp!

Yup - upfront cost - same like my jointer. I would have sent my blades out 5 times on my old jointer and still on the 2nd side of my 1st set of knives on my helical jointer.

[Bill Space]

Just an after thought...but I found that using a bowl type bit, that has rounded edges, rather than a bottom cleaning bit, that has square edges, works better for me.

Less sanding to get rid of the lines between where the router bit went.

YMMV...just my limited experience...

Edit: after posting I had to look back and see if my post made any sense. I think it might...

Hope sollll

[John TenEyck]

I'm still using a 2" Yoniko spoilboard bit that I paid something like $15 for about 6 months ago. I've flattened quite a few hardwood slabs with it. Just sayin'.

John

[Justin Rapp]

Well this was a long awaited project with tons of other things in the mix but I finally got the rails, plus my in-laws friend was moving and asked if I wanted his router table setup. It was small and home built, but housed a 1617evs motor. I just need to get a base for it.

Hopefully if time allows I'll finally get this this built.