I face many problem on shipping module, hope all experts here can guide me to solve it

I set Configuration/Shipping/Packaging/Maximum Package Weight = 20KG
and this is my table rate for zone 1:
0.5:21.34,1:26.51,1.5:31.68,2:36.85,2.5:42.02,3:47.19,3.5:52.36,4:57.53,4.5:62.70,5:67.87,
5.5:73.04,6:78.21,6.5:83.38,7:88.55,7.5:93.72,8:98.89,8.5:104.06,9:109.23,9.5:114.40,
10:119.57,10.5:124.74,11:129.91,11.5:135.08,12:140.25,12.5:145.42,13:150.59,13.5:155.76,
14:160.93,14.5:166.10,15:171.27,15.5:176.44,16:181.61,16.5:186.78,17:191.95,17.5:197.12,
18:202.29,18.5:207.46,19:212.63,19.5:217.80,20:222.97


My problem:
1) since I set max packaging weight is 20KG, why customer still can buy product more than 20KG and proceed to payment?
2) if I remain database configuration_value varchar=255, table rate will chop at 13KG, weight more than that will display as below, but the problem is it can proceed payment with $0, any way to solve this problem?



3) if I extend database configuration_value varchar to 9999, after 20KG, it will display random rate for worldzones rate, example when total product weight is 21KG, but world zones rate display 10.25KG rate.

Hope someone can help me to fix this.

1. setting a 20kg shipping rate doesn't prevent a purchase of an order over 20kg, it just means you've only set a cost for an order <20kg and it'll box any order up into boxes of <20kg

2. you need to set a catch-all rate above 20kg, eg 999:1000
generally if 1) you're getting orders for over 20kg, you haven't really consider what you're selling (that rates table looks very complicated, try simplifying it - most customers hate shipping regardless of graduations, so you're not doing it for them); 2) seeing $1000 for a 20kg+ order will generally put off most people

3. see point 2. changing a table field to varchar 9999 won't work (it's 408 characters in that long version of rates anyway so why 9999? crazy)

Simon

I have multiple product, some product very light, but some quite heavy, i am not sure customer will buy item more than 20kg or not, just to prevent if they buy item more than 20kg, it will be free shipping and cause my loss. I have think to use something as u mentioned like $1000 for above 20kg.
i change to 9999 because there is another shipping method is adding rate every 100g , this is why i ask for any other method/formula to write table rate in simple way at another post.

It would be pretty silly to try and prevent customers from placing an order over a certain amount, just because the box logic in the cart can't handle what you need. So my advice is to get a coder to edit the shipping class so that the box logic you need works better.

Please refer to the other post you made.

Simon

i understand that,29KG is just an example, actually i have multiple shipping options for customer, example 2 types of air mail ( table rate below 2 kg and table rate for heavy parcel) + few courier services. this is my 1st time using shipping module, so I need to try everything to sort out all the problem i facing one by one.

thanks for your guide, i will study code at /includes/classes/shipping.php which u post at another thread.