Help Please

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This is an idiots question Im afraid. I want to router some grooves 18 mm Mdf. for a book shelf - just a narrow one. In the past I have used an 18 mm router bit and it is never the snug fit logic would suggest. Not my technique - somewhere in the back of my mind years ago I believe I heard that you had to use a smaller router bit. Could someone tell me what size I should be buyng when I go to the shops over the weekend
Thanks for any help - Keith
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keef wrote:

If you are not getting an 18mm recess in the MDF and the bit is definatly 18mm?this is because there is slight play on the rotor shaft. Best bet is to aquire a 12mm and route a 12mm recess then carefully route out just under 6mm recess next to the 12mm one. Dont go right up to 6mm a fraction before 6mm and the excess can be sandpapered out as MDF is an easy material to sand.
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Sir Benjamin Middlethwaite




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If you like extra work but a better finish, then rout a 12mm dado in the one piece and rout a 6mm rabbit on the edge of the shelf so the upper edge of the shelf meets the side of the case with a nice clean butt joint and the 12 mm tounge below fits into the dado. You can adjust the depth of the rabbit to get the shelf just as snug as you like in the dado. This is a pretty common technique on CNC built cabinets.
keef wrote:

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SonomaProducts.com wrote:

Would that be the bit with the long ears and fluffy ball tail?
--
Sir Benjamin Middlethwaite




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I no, I cen nevur re-member witch spellin two youse. "I jus ain't that good a speller"
BW The3rd Earl Of Derby wrote:

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SonomaProducts.com wrote:

Try installing a dictionary to coincide with your newsreader then. :-)
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Sir Benjamin Middlethwaite




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If you like extra work but a better finish, then rout a 12mm dado in the one piece and rout a 6mm rabbit on the edge of the shelf so the upper edge of the shelf meets the side of the case with a nice clean butt joint and the 12 mm tounge below fits into the dado. You can adjust the depth of the rabbit to get the shelf just as snug as you like in the dado. This is a pretty common technique on CNC built cabinets.
keef wrote:

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Thanks for the information and guidance. The router I am using has had little use so what you both appear to saying is that there should be no problem if I use an 18mm bit and I shouldnt have the 2mm or more play - is that right - if that is the case I am inclined to go buy another and see what happens. If this does not work try the 12 and 6 method. What do you think?
Whilst I am here do you have any good links I could follow re Kitchen work tops - joining at the corners of the room.
Thanks for everyones help
Keith SonomaProducts.com wrote:

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keef wrote:

A router can be brand spanking new out the box,but its performance relys on whether its an expensive one or a cheapo. If its a cheap one then chances are the internal working parts are of poor quality.
Whats the router you have?
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Sir Benjamin Middlethwaite




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Miter bolts. http://wwhardware.com/catalog.cfm/ProductID/KV0516%20100
keef wrote:

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Thanks again - the router should be okish it is sold in England by Wickes - which is a DIY outlet - I appreciate that it would not be in same league as others but it should really not be that bad - but who knows really. I have been looking out for a Dewalt - any recommendations whilst Im here.
Thanks again
Keith - Just a simple serf in this kingdom
SonomaProducts.com wrote:

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keef wrote:

There lies your problem then...Wickes own brand. :-(
Any of the De-Walt routers are good enough,preferably the 1/2" collet range though. Makita and bosch you should also look at although bosch is within most peoples budget.
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SonomaProducts.com wrote:

That's the technique I use on all my selves. I rout a 1/4 inch dado and then a roughly 1/2 inch rabbit. It works really well on plywood, as the thickness of the sheets vary from batch to batch. Therefore, all the pieces become interchangable.
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bf wrote:

For gods sake its called a...
Rabbet.
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wrote:

One thing I like to do when routing dadoes is to pre-rip each side of the dado on the table saw, then use a smaller bit to rout it freehand. That way, you know that the dado is straight, (and not messed up because of a damaged or warped straightedge) any chance of tear-out is eliminated, and the kerf from the saw gives you enough room for error to make freehand routing a viable option. Even if you still use a straightedge or a table, it's still useful for controlling tearout (not a problem in mdf, but I assume you'll be making other projects in the future.)
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Prometheus wrote:

The quickest way I do it is by using two 5mm aluminium straight edges spaced a thou or two less for the desired width then an appropriate guide bush attached to the router and guide bush fed the router along the straight edges in MDF.
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The3rd Earl Of Derby (in 6oc_g.38898$ snipped-for-privacy@text.news.blueyonder.co.uk) said:
| The quickest way I do it is by using two 5mm aluminium straight | edges spaced a thou or two less for the desired width then an | appropriate guide bush attached to the router and guide bush fed | the router along the straight edges in MDF.
That should work well. Leon devised a most ingenious jig for routing dados with extreme accuracy. I've posted his photos and a drawing of my own at the link below.
-- Morris Dovey DeSoto Solar DeSoto, Iowa USA http://www.iedu.com/DeSoto/dado.html
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Morris Dovey wrote:

Similair to the Ally one I made except mine is a lot less bulky when stored or put away.
The Ally jig is 4"wide by 5mm thick and 3' long.
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wrote:

Well, there goes my argument for the table saw kerf making sure the dado is square to the edge. Nice design, Leon- I might make one of those myself.
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Prometheus wrote:

But there's a flaw in Leons design,anyone spot it?
Sorry Leon.
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Sir Benjamin Middlethwaite




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