Why a slight crown? - Router Forums
Reply
 
LinkBack Thread Tools Display Modes
post #1 of 11 (permalink) Old 04-26-2010, 11:57 AM Thread Starter
Registered User
 
Join Date: Nov 2008
First Name: Glen
Posts: 1
 
Default Why a slight crown?

Hi all...my first post...thinking of starting by building a router table.
I'm interested in the Trend insert plate to slot into the table top.
The ad mentions that it is "Moulded with slight crown (0.8mm) for distortion free cuts"!
Can someone explain what this means.

Thankyou

Regards
Gerry
wotarout is offline  
Sponsored Links
Advertisement
 
post #2 of 11 (permalink) Old 04-26-2010, 02:13 PM
On vacation
 
Join Date: Apr 2009
First Name: Joe
Posts: 189
 
Default

I believe it means that the manufacturer is either incapable of manufacturing a perfectly flat plate or is trying to sell it at a price point that prohibits it.
In either case a "slight crown" is NOT preferable. NOTHING is better than perfectly flat. Period.
Save your money and invest in a quality plate by a reputable manufacturer like Kreg, JessEm, Woodpecker etc.
jmg1017 is offline  
post #3 of 11 (permalink) Old 04-26-2010, 03:14 PM
Registered User
 
Join Date: Jun 2009
Country: United States
First Name: Danny
Posts: 655
 
Default

I agree get a plate that is flat, .008 mm crown???? my guess is that would be about a 1/32" bow or crown. Not the best for a router table.
jd99 is offline  
Sponsored Links
Advertisement
 
post #4 of 11 (permalink) Old 04-26-2010, 04:49 PM
Registered User
 
Cassandra's Avatar
 
Join Date: Mar 2006
Country: Canada
First Name: Cassandra
Posts: 787
 
Default

I wonder how the phenolic plastic will flex when one hangs a 2-1/4 hp or 3 hp router under it.

Carpe diem, quam minimum credula postero
http://www.panoramio.com/user/5924351
Cassandra is offline  
post #5 of 11 (permalink) Old 04-26-2010, 08:58 PM
Retired Moderator
 
BigJimAK's Avatar
 
Join Date: Mar 2009
Country: United States
First Name: Jim
Posts: 3,503
     
Default

The flex will be *downward*, Cassandra; the amount is a calculation left to the student.

Check out that new high-tech cordless router.. wireless and no recharging required!!
BigJimAK is offline  
post #6 of 11 (permalink) Old 04-27-2010, 07:21 AM
Registered User
 
Cassandra's Avatar
 
Join Date: Mar 2006
Country: Canada
First Name: Cassandra
Posts: 787
 
Default

Hi Jim:

Yes, the deflection is of course downward. My previous post was to stimulate the conversation on whether the slight crown would disappear once the router is hung.

Cassandra

Carpe diem, quam minimum credula postero
http://www.panoramio.com/user/5924351
Cassandra is offline  
post #7 of 11 (permalink) Old 04-27-2010, 07:33 AM
Registered User
 
Join Date: Jun 2009
Country: United States
First Name: Danny
Posts: 655
 
Default

Yep but being plastic, the deflection wouldn't stop at flat, it would continue downward over time and with heat then you would have a concave spot in the table.
jd99 is offline  
post #8 of 11 (permalink) Old 04-27-2010, 10:42 AM
Retired Moderator
 
BigJimAK's Avatar
 
Join Date: Mar 2009
Country: United States
First Name: Jim
Posts: 3,503
     
Default

Deflection is the key, Danny, and Cassandra's point... <going technical here all.. skip the rest if you don't want to read technical>

when you hang a weight on a flat plate, to exert its lifting force it bends downward slightly. It's the compression force on the top and the tensile force on the bottom that provides the "lift". Just how much it deflects depends upon many things such as thickness, distance to support and properties of the material used. As long as the weight doesn't exceed the "elastic deformation" range and move into the "plastic deformation" range, it will spring back when the weight is removed.

Thus technically, if you want it to be perfectly flat with a weight on it there should be some amount of crown on it without weight such that after the load is applied it becomes flat. In practice, for a rigid plate that's not excessively large and not too heavy of a weight, that amount is insignificant and can be ignored.

For an easily visualized example of this, consider a long overloaded bookshelf. It sags in the middle. If it were designed with a slight crown in the middle and the ends were constrained (held) from moving outward, it could hold a lot more weight. This principal is what makes arched entries so much stronger than square ones and why a lot of the Greek stonework (with arched brick construction) are still standing today.

<end technical>

Check out that new high-tech cordless router.. wireless and no recharging required!!
BigJimAK is offline  
post #9 of 11 (permalink) Old 04-27-2010, 12:26 PM
On vacation
 
Join Date: Apr 2009
First Name: Joe
Posts: 189
 
Default

Interesting, but why try to estimate such things?. Buy a high quality 3/8" plate that is flat and won't deflect from the weight of the heaviest router you plan on installing.
jmg1017 is offline  
post #10 of 11 (permalink) Old 04-27-2010, 02:27 PM
Retired Moderator
 
BigJimAK's Avatar
 
Join Date: Mar 2009
Country: United States
First Name: Jim
Posts: 3,503
     
Default

That's what I did, Joe.. As I said above, I considered it insignificant...

Check out that new high-tech cordless router.. wireless and no recharging required!!
BigJimAK is offline  
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Router Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in











Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Similar Threads
Thread Thread Starter Forum Replies Last Post
Crown Molding nblumert Router Bits - Types and Usage 6 08-14-2009 09:54 AM
Best bits for crown molding? rstermer Router Bits - Types and Usage 35 02-13-2009 09:21 PM
Use for crown staples? Birchwood Tools and Woodworking 6 12-20-2005 08:31 PM
Curved crown moldings Alex Cantacuzene Portable Routing 5 10-29-2005 11:25 PM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome