Cutting list optimisation algorithm

[MikeSharp01]

We have 312 lengths (elements) of timber in our frame mainly I-Joist (FJI) and Kerto beams but some 38 x 89 C24 and some Gluelam. I have exported the details of each element from the frame drawings to a spreadsheet and now need to opimise the order from standard lengths (8m /10m / 12m) anybody come across an algorithm for doing this?

 

Can write it in any language but VBA is simplest given everything is in the spreadsheet. I have had a look at the commercial packages and they seem mostly focused on flat sheet cut optimisation which is not my problem right now. I don't want to go to the work of creating a Genetic or algebraic optimiser so I am hoping a simple algorithm will get me close enough as I would like to keep the costs in control and I will add a few standard lengths of each size to the order

 

My basic approach is going to be:

Settings like: Cut margin (The amount to add to the length for cutting - 10mm perhaps)

Then

Repeat

   Set cut length to Zero

   Seek longest remaining element and set element spec IE '58x220 FJI' or '75x240 KERTO'. 

   Add to cut length

   Repeat

       Define Waste from standard length(s)

       Find nearest fit, allowing for cut margin, from remaining items

       Add to cut length

   Until cannot find any more that can fit in the waste

   Add standard length found to order sheet

   Record final waste figure

   Flag all elements assigned as not remaining and mark them against the standard length code (So I know what I am cutting from each length)

Until all elements assigned to a standard length

Add up final waste figures

 

Feels about right, will run it three times, once for each standard length and see what the waste is on each - sure not perfect though.I guess there is always a chance the supplier might optimise it for me but thought I would have a go myself.

 

Any thoughts anyone. 

[PeterW]

I use this Cutting List Calculator

 

 

[MikeSharp01]

Thanks Peter, I think that will be a lot of typing as it does not seem to accept mass entry (CSV etc) - interesting roots though in cattle markets and it seems to roughly apply the algorithm I suggested!

[ultramods]

just wondering are the standard 8,10, 12 m standard lengths all the same price per linear metre as this might affect the algorithm if they aren't.

 

Also where are the cuts taking place at the suppliers factory or somewhere else? If somewhere else you way want to avoid 8m or 12m standard lengths if no single beam is going to be greater than 6 m in terms of the type of transportation used.

 

Edited August 27, 2018 by ultramods

[MikeSharp01]

2 minutes ago, ultramods said:

just wondering are the standard 8,10, 12 m standard lengths all the same price per linear metre as this might affect the algorithm if they aren't.

My initial forays in prices seems to indicate that the 10m lengths are the cheapest per meter - could be something to do with transport, but I will check that with the competing suppliers, thanks for pointing it out.

[ultramods]

1 minute ago, MikeSharp01 said:

My initial forays in prices seems to indicate that the 10m lengths are the cheapest per meter - could be something to do with transport, but I will check that with the competing suppliers, thanks for pointing it out.

I had just edited my post to include something about transportation costs

 

[Ed Davies]

I took my cutting list of C24 for the floor to a local timber merchant (branch of Rembrand Timber). To my surprise the manager there worked out a list of standard sizes by hand (didn't have software to do it). To be honest, though, I don't think it's worth trying to be too clever; in practice the wood will have dings and all sorts of practical issues like what's piled where means you won't use them in the right order anyway. Just pick a couple of standard sizes which mostly work and be a bit careful how you use those.

 

E..g, for the joists for the last two rooms (http://localhost/2018/06/gable-start/) the bathroom needed a bit less than 2.4 m lengths and the small bedroom needed just over 2.4 m. I was short of the timber for a few joists so order half a dozen bits of 4.8 then had to remember not to just do all the bathroom ones as I couldn't get two bedroom ones out of a 4.8. If the bathroom ones had had to be paired up like that with the living room joists (the room I did first) then simply keeping track of which offcuts needed to be kept for what would have been tricky.

 

Apart from anything else, extra offcuts will be useful as dwangs/noggins (see, I'm bilingual!).

Edited August 27, 2018 by Ed Davies

[MikeSharp01]

1 minute ago, ultramods said:

I had just edited my post to include something about transportation costs

Yep just spotted that, cutting will take place on site, for the garden room we used 10m lengths and that came on a pretty standard lorry I thought although no HIAB so had to move them all by hand.

[MikeSharp01]

1 minute ago, Ed Davies said:

Just pick a couple of standard sizes which mostly work and be a bit careful how you use those.

Yes - sensible approach but I don't yet know how many of each standard size need so at least my algorithm will tell me that approximately I worry that just dividing the total length needed by the standard length will result in more wastage as I will have to order extra to be sure to be sure! 

[Thedreamer]

Our house is stick build, so I've had to order a fair bit of timber.

 

I just worked on the stock lengths of 4.8m.

 

You always need offcuts for scaffolding or on top of tarpaulins etc.  

 

I was surprised how little it costs to frame a property, I think it was around £10k (for all the timber, OSB, sarking boards and breather paper) and £5k was for the attic trusses and the truss grade wood. 

[Russell griffiths]

Who have you had prices from for your I joists @MikeSharp01

i have just had some prices back for my roof which will be all I joist

they are actually cutting them all to the design length 

i don’t know whether this is more cost effective or not

did you have a price to cut them all to your cutting list. 

[MikeSharp01]

1 hour ago, Russell griffiths said:

Who have you had prices from for your I joists @MikeSharp01

i have just had some prices back for my roof which will be all I joist

they are actually cutting them all to the design length 

i don’t know whether this is more cost effective or not

did you have a price to cut them all to your cutting list. 

 

I didn't ask for cutting as I am not sure they can cut them accurately enough and most of them have angles on the end. However when the job goes in for quotes it will include a cuts spec so they can price it provided that can meet the tolerances. 

[bissoejosh]

21 hours ago, MikeSharp01 said:

 

I didn't ask for cutting as I am not sure they can cut them accurately enough and most of them have angles on the end. However when the job goes in for quotes it will include a cuts spec so they can price it provided that can meet the tolerances. 

Our I-Beam frame was cut by Severn Valley Timber prior to delivery. Everything from notching the ridge beam where rafters land, sole plates for stud positions etc was perfect. You need a machine file for them to work from and we used Cullen Timber Design for this. Both highly recommended. 

Edited August 28, 2018 by bissoejosh
wrong company name

[Russell griffiths]

Did you mean Severn Valley woodworks @bissoejosh

as im struggling to find any other. 

[bissoejosh]

Certainly did, apologies..

https://www.svw2000.co.uk