Another sled question

[Halo Jones]

I am also wanting to make a cross cut sled for my table saw. All the guides I have seen use 12mm ply but I only have 9 or 18 mm available and don't have the room to buy a sheet of 12mm when I will only use a third of it.

So 9 or 18 (hammer)

H.

 

[MickCheese]

I used 9mm for mine and bolstered it up by making the bridge pieces from some recycled mahogany desk legs, they kept it flat.

Mick

 

[Sportique]

Halo - I have a piece of 12mm MDF that you are welcome to collect - in Leven.

If interested drop me a pm.

Dave

 

[Halo Jones]

Hi Dave,

That is most generous but my workshop qaudruples as storage for bikes, garden stuff, other stuff and even more other stuff and is full #-o . I need to build some stuff with what I have so I have some room to build stuff!!!!

btw. pleased to meet another Fifer on the forum; most of my family is from the Leven, Methil, East Weymss area but l now live in the Howe and for my sins work in Dundee :twisted:

It seems there are quite a few Fifers on this forum. I often think it would be good to have a fife ukworkshop bash. I might even learn how to do some woodworking!!

H.

 

[Steve Maskery]

9mm is OK. The bridges should keep it flat. You can also use the 18mm but you will lose more depth of cut. It depends on what material you are cutting and how big the saw is.
S

 

[Sportique]

Hi Dave,

That is most generous but my workshop qaudruples as storage for bikes, garden stuff, other stuff and even more other stuff and is full #-o . I need to build some stuff with what I have so I have some room to build stuff!!!!

btw. pleased to meet another Fifer on the forum; most of my family is from the Leven, Methil, East Weymss area but l now live in the Howe and for my sins work in Dundee :twisted:

It seems there are quite a few Fifers on this forum. I often think it would be good to have a fife ukworkshop bash. I might even learn how to do some woodworking!!

H.

Hi Halo,

I know what you mean about workshop space and bikes etc ...

Yes, there are a number of members in Fife.

Dave

 

[wcndave]

Tolerences... I finally made one with many struggles that i won't document, however, i now have 2/1000 across 50" using 4cut technique. Seems reasonable to me, any thoughts? Running out of space to put new holes!

 

[Halo Jones]

That seems pretty good to me. I don't think you will notice it over a 2 or 3" crosscut! I can understand the frustration in getting it right. my problem was the screws breaking as I tried to remove them from the fence #-o and I also managed to split the end of one of the slide rails as I put in the last screw - just had to remove the screw and cut a couple of inches off the end.

Mine scares the devil out of me at the minute as I have still to put a perspex guard on and a box on the where the blade exits the rail. I don't know how people can use them without any of these. Maybe I'm just a wimp!

H.

 

[Steve Maskery]

That would do for me, too!.
You don't have to keep making new screw holes to remount the fences, though. With a bit of forward planning you can put little brass screws in the runners and tweak them in and out as required. This is FINE adjustment, though. If you start too far out you will end up with an accurate xcut sled with a kerf as wide as the English Channel. But it does work very well and it's how I did the one on my DVD.
Guards and exit boxes are not optional!

 

[wcndave]

I am not sure how screws in runners will help align the fence. I've seen a few of your jigs where you use similar techniques, which all make sense.

In this case, it is the squareness of the fence.

I have the runners on and fairly good fit, a bit of binding, however that is down to my saw more than anything else. I then raise the blade through it, and the kerf "should" never change, as the blade to runners to base is fixed.

Then i attached the fence as square as i could manage by using square against the slot i'd just cut, cut 4 times round a board, found i was out by 12 thou, added a shim of 3 thou, rescrewed one end of fence, was out by 4, same again, and was sorted, 2 thou over about 4 feet.

the really odd thing is that i then wanted to make a 45 deg mitre attachment, and started with a square, which i cut in half to get "close enough" to 45%, figuring i would use one angle for half the mitres, and the other for the other half, so if i had 45.5 and 44.5, they would still fit perfectly and be undetectable to the eye.

It did not work, so i check the 90 deg angle, as that is the only one that has to be right, right? and we all know that the corners of a triangle add up to 180 deg.

well, i have invented new trigonometry, as according to my red gem 0.1deg digital angle measuring thingy, calibrated at 0 deg on a planer bed, and 90 deg with a good square, and double checked numerous times... i have angles of 90, 45.4 and 45....

 

[Steve Maskery]

I am not sure how screws in runners will help align the fence. I've seen a few of your jigs where you use similar techniques, which all make sense.

In this case, it is the squareness of the fence.

I have the runners on and fairly good fit, a bit of binding, however that is down to my saw more than anything else. I then raise the blade through it, and the kerf "should" never change, as the blade to runners to base is fixed.

Then i attached the fence as square as i could manage by using square against the slot i'd just cut, cut 4 times round a board, found i was out by 12 thou, added a shim of 3 thou, rescrewed one end of fence, was out by 4, same again, and was sorted, 2 thou over about 4 feet.

That is a perfectly good way to do it. Another way would be to make the fence in two parts and shim between them. The screws-in-runners method does work well, too. They effectively rotate the whole sled.

the really odd thing is that i then wanted to make a 45 deg mitre attachment, and started with a square, which i cut in half to get "close enough" to 45%, figuring i would use one angle for half the mitres, and the other for the other half, so if i had 45.5 and 44.5, they would still fit perfectly and be undetectable to the eye.

It did not work, so i check the 90 deg angle, as that is the only one that has to be right, right? and we all know that the corners of a triangle add up to 180 deg.

well, i have invented new trigonometry, as according to my red gem 0.1deg digital angle measuring thingy, calibrated at 0 deg on a planer bed, and 90 deg with a good square, and double checked numerous times... i have angles of 90, 45.4 and 45....

Hmm. I don't think Thales has much to worry about! There are several possibilities. Sides not straight, not fixed to base squarely, your doo-dah not as precise as you think... It must be something like that, I'm sure. The only thing that matters is - does the final joint work?
S

 

[wcndave]

Final joint is "good enough", however not perfect. I might take a few pictures of the whole process.

 

[Steve Maskery]

Remember that for a mitred frame, it's not sufficient for the cuts to be 45 deg, the opposite sides must be exactly the same length, too. But you knew that already
S

 

[wcndave]

ah.... that explains it, i had 12", 14", 16" and 18" pieces, and those pesky 45 deg angles just weren't working out for me.....

biggest problems I had were:

- cutting and fitting accurate runners when they are 8mm x 13mm
- the fact that the fence rails on back and front were higher than the slots!
- the fact that the outfeed table makes the slots "stopped" slots, with no way to adjust
- raising a blade through a base with the riving knife still in place #-o

 

[Steve Maskery]

Hmmmmm...........

 

[The Bear]

Can anyone post a link to the 4 cut technique mentioned above please


Mark

 

[Steve Maskery]

Well I could, but I'm not allowed to! You'll have to follow the footer.
And actually it is five cuts, but that is being picky


S

 

[wcndave]

Loads of examples on the web, but basically you make your sled, then take say a 24" square board and cut all 4 edges, and then if you are steve you can cut an extra one for good measure

Each time you place the just cut edge against the fence.

The end result is that your error is magnified by 4 (5), so a 2 thou error over 12" which is hard to detect, becomes 16 thou when you've cut all the way around. (24x4 = 96")
(Try putting a 96" board in your table sled lengthwise for accuracy purposes!)

To measure the error, i cut the last "offcut" strip about 1" wide, mark front / back before i pick up, and use digital calipers to check the front width compared to back.

it's really easy method, especially if you have some scrap wood. You should not aim to get it perfect, i think my 2thou over that distance total is fine.

The woodwhisperer has a good video on making a table sled, which is the technique I followed. I absolutely KNOW that steve has the best one ever on his DVD ;-)

Dave


[please note all opinions are that of the poster only and do not reflect reality etc....]

 

[Steve Maskery]

Actually mine is a bog standard one. I don't claim any innovation about it at all.

But the reason I cut 5 rather than 4 is that it ensures that I am measuring against a known straight edge. That piece we are measuring then has two fresh sawn edges that we know are good. It's only a small point but it saves the embarrassment of of measuring at just the point where it's had a ding and throws the error out too far.
S

 

[wcndave]

yer, but it's the way you make it ;-)