4mm dado cuts

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Forum topic by DTrak posted 01-21-2017 06:20 PM 821 views 0 times favorited 17 replies Add to Favorites Watch
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58 posts in 1183 days

01-21-2017 06:20 PM

Topic tags/keywords: dado cuts

This isn’t exactly joinery but wasn’t sure where else to post. I am sliding panels of glass into dado cuts. The glass is only about 2.5mm thick, so I need my dado cuts about 4-5mms thick. I have a common Dewalt plunge router with 1/2” shank. I can’t find any bits that are smaller enough. I can use a table saw, but the dado cut has to stop halfway through the wood with a flat bottom edge for the glass to sit on, so the round cut of a table saw wouldnt work. Any ideas? thanks

17 replies so far

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937 posts in 1527 days

#1 posted 01-21-2017 06:40 PM

You may need a 1/4” collet or a 1/2-to-1/4 adapter to get a bit that small into your router.

Many bit manufacturers offer a 5/32” (3.97 mm) or 3/16” (4.76 mm) in 1/4 shank, such as:

Infinity Tools

-- Jerry, making sawdust professionally since 1976

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58 posts in 1183 days

#2 posted 01-21-2017 06:54 PM

Thank you! You nailed it. I just looked through the router bag and realized it even came with a 1/4” collet! I will buy one of the ones you mentioned.

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2494 posts in 985 days

#3 posted 01-21-2017 07:17 PM

Have you considered a slot cutter.
I think it would be small enough not to run out the end and also I think would be easier to use.

View jdh122's profile


1032 posts in 2903 days

#4 posted 01-21-2017 07:51 PM

I’ve had pretty poor luck with the very small router bits. You have to take very shallow cuts as they snap off really easily. I’d be inclined to use the tablesaw and then square up the cut with a chisel (although come to think of it, 4 mm is a pretty small chisel).

-- Jeremy, in the Acadian forests

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58 posts in 1183 days

#5 posted 01-22-2017 12:06 AM

I don’t know what a slot cutter is. I will look into it.

The problem with a table saw is the round cut gets more and more gradual, hard to square off. I have seen chisels that small though.

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2494 posts in 985 days

#6 posted 01-22-2017 12:13 AM

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58 posts in 1183 days

#7 posted 01-22-2017 02:08 AM

Does it work like a router?

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2494 posts in 985 days

#8 posted 01-22-2017 02:44 AM

Yes, you put it in your router and use it the same as you would any bit. It cuts a slot, (from the side) and you can buy the cutters in the different widths (4mm) that you need.
I just used one the other day and it’s still in the router. I’ll take a picture tomorrow morning and show you what I did.

Here is a youtube video of one being used.
The one in the video is pretty thin, you would have to find one the size you need.

View AlaskaGuy's profile


4274 posts in 2395 days

#9 posted 01-22-2017 08:07 AM

Be careful using thin slot cutters. The wings will bend very easily. When one bends it no longer cuts the same size slot.

-- Alaskan's for Global warming!

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237 posts in 619 days

#10 posted 01-22-2017 11:53 AM

Do you have a tablesaw blade that has a square tip grind?

These will give you a flat bottom cut. Consecutive side by side cuts will give you the size needed.

If you don’t have one, try an ATB (Alternate top bevel) grind, glue sandpaper on a scrap the correct thickness and just sand out the ridge.

-- nice recovery, They should pay extra for that mistake, Eric E.

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8295 posts in 2662 days

#11 posted 01-22-2017 01:03 PM

The metric standard set includes the small plow plane with 1/4” blade plus 4mm, 5mm, 6mm, 7mm, 8mm and 10mm blades.,230,41182

Have some fun and increase your hand planing skills.

View splintergroup's profile


2210 posts in 1308 days

#12 posted 01-22-2017 03:36 PM

I’d use a slot cutter bit on a router table, but they do leave the same gradual curve at the end like a table saw blade would do (2” or so diameter versus the TS 10” diameter). This curve can then quickly be cut away with the above mentioned small router bits.

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Steve Maskery

48 posts in 3470 days

#13 posted 01-22-2017 04:30 PM

You certainly could use a wing slot cutter and tidy up the ends by hand. You could grind down an old 1/4” chisel to 4mm quite easily.
But is there any reason why you cannot cut the slot right through and then fill the the end with a strip? It would be very easy and, if you did it well, virtually invisible. That’s what I would do.

-- The Complete Tablesaw -

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2494 posts in 985 days

#14 posted 01-22-2017 04:58 PM

Here is the bit I just used. It has quite a bit thicker plate than the thin one in the video above.
I’m not too worried about it bending as Alaska guy mentioned. (I’m also using a 1/4” cutter).

Here is the slot it cut,

I’m making some sliding closet doors and this is for the track in the bottom.

View DTrak's profile


58 posts in 1183 days

#15 posted 01-22-2017 06:53 PM

Thanks all! I already bought the smaller router bit, so I will try that first, but it’s good to know about the slot cutter too. I can’t fill in part of the slot because this is all visible. thanks again

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