Lam stack calculator

[jess stuart]

I am a computer idiot so, keep that in mind.  My PC is very close to dying.  Question can you use the lam stack calculator on a chromebook?

[Kirkll]

The lam stack calculator was created on an excel spread sheet. i have no idea whether it will function properly on a chromebook. i suppose it would depend on what software you are running on it..... Give it a go and see....

[VTer]

Where do you see the lam stack calculater

[Burnsie]

Chrome book has its own spread sheet software - I've had mixed results with more complicated Xcel sheets importing and keeping all the formatting.

[Kirkll]

https://support.microsoft.com/en-us/office/how-to-access-microsoft-365-on-a-chromebook-32f14a23-2c1a-4579-b973-d4b1d78561ad

[Kirkll]

You could easily build your own lam stack calculator on your existing spread sheet software. It’s just basic mathematics and calculates different draw weights and stack heights using percentages and adds or subtracts the difference.

Kirk

[Brian from GA]

There are "forecast" formulas that are linear interpolation functions for that.  You could do a column for stack height with a corresponding draw weight column for just a few known bows and it will inter/extrapolate for any other stack you put in for the input.

[Mad Max]

Where do you see the lam stack calculater

You have to get it from someone. You need Xcel on your computer
PM me your e-mail address and I will send it to you

[Kirkll]

I use mine from time to time when I don’t have anything in my log book close enough, or I miss draw weight real bad on one like I did yesterday. 

I had one targeted for 53-55 @ 30” and wanted it 58-60# rough draw weight out of the form, and it came out 73#.    

Never ceases to amaze me how every now and then ya just get one that comes in heavy like that for no good reason at all…. I’ve built 300 sets of limbs just like these…..

But…. Using the  same materials I just used, the lam stack calculator typically works excellent on a second go round.    Kirk

[mmattockx]

There are "forecast" formulas that are linear interpolation functions for that.  You could do a column for stack height with a corresponding draw weight column for just a few known bows and it will inter/extrapolate for any other stack you put in for the input.

But limb bending stiffness (which is what you are calculating) isn't a linear function. Linear interpolation would probably work OK if your data points are pretty close together and you never try to go very far outside your existing range, but it will be limited if you are off in new territory by much.

You have to get it from someone. You need Xcel on your computer

These days you don't even need Excel itself, there are free open source spreadsheets that will run Excel files. Office Libre usually works pretty well for this.


Mark

[Brian from GA]

There are "forecast" formulas that are linear interpolation functions for that.  You could do a column for stack height with a corresponding draw weight column for just a few known bows and it will inter/extrapolate for any other stack you put in for the input.

But limb bending stiffness (which is what you are calculating) isn't a linear function. Linear interpolation would probably work OK if your data points are pretty close together and you never try to go very far outside your existing range, but it will be limited if you are off in new territory by much.

Yeah, that's true, but the range of usable bows is concise enough that you don't really run into that at least with long bows.  I did a chart modeled of binghams numbers and the curvature could be considered negligible from 35-70. I them used forecast and was within #.5 for most any useable weight for a given stack.  Not to mention, the forecast gets better everytime you add data. I think it's a weighted function, so it isn't strictly" linear".

[Kirkll]

Here’s the straight poop….. you can build all the “Air bows” you want and play with the high tech engineering software to “Forecast” the end product using different limb shapes…. But…. And it’s a BIG BUTT….. once you roll up up your sleeves and start actually building and testing these different designs, that reality is a whole different ball game. Hand on experience with a detailed bowyers log trumps Air Bows and extrapolating forecasted results any day….   Kirk

[Brian from GA]

Yeah that's true without a doubt. I didn't think anyone's trying to argue against that point.  I've probably only got 50-60 laminated and selfbows under my belt, but only about 10 glass bows. For me I love building as much as shooting, but each build is a financial investment to some degree, and building new forms to play with different designs is a straight up question mark for where to even start work a stack because I don't have that log book. Air bows help me think it out. I'm playing with a recurve design and Hill style design right now. I'm definitely going to make sure they're good "air bows" before I sink a couple hundred dollars and a weeks worth of work into it. I'm all for rolling up my sleeves, but I hate wasting time and resources and some of these things are just good tools to help me think through things before I jump in head first.

[Kirkll]

Right on brother... i get it.   Just be sure and take the time for detailed log entries of everything you build... It's taken me 15 years of building glass bows to accumulate all my data, and it's priceless. 

[Brian from GA]

I got the old trusty dusty black and white jornal pad.  I'm working on writing a little built to purpose phone app for it.  The notepad doesn't like the shop humidity.  It's very limp lol.

[mmattockx]

Here’s the straight poop….. you can build all the “Air bows” you want and play with the high tech engineering software to “Forecast” the end product using different limb shapes…. But…. And it’s a BIG BUTT….. once you roll up up your sleeves and start actually building and testing these different designs, that reality is a whole different ball game. Hand on experience with a detailed bowyers log trumps Air Bows and extrapolating forecasted results any day….   Kirk

Kirk,

I disagree. Reality is NOT a different ball game. The point of engineering is to be able to predict reality. When a structure is built these days we don't build a test version and see what it can carry for load before it collapses, we design it on paper and KNOW that it will work.

I agree 100% that you need to verify design calculations with actual bows to confirm that predictions are correct. Verification is a necessary part of the process. But once that is verified it lets a designer work on paper without having to build every last version to see what happens. It is a more efficient way to test ideas than building one of everything. As you have noted, there are endless combinations and permutations of bow design details. Being able to predict the effect of even some of them saves a lot of effort in the workshop.

To really get somewhere you need some of both methods. Design will get you so far and then you have to do some building and testing to refine other details. It all works together to produce the end result.


Mark

[Kirkll]

Well we'll just have to agree to disagree on the engineering and air bow calcs being a necessary or even an important factor of building bows and testing different designs. The point i was trying to make is that you can do the super tiller calcs on the best energy storage and best limb shape to accomplish this, and once you actually build it , you find that it's vertically unstable and has floppy limbs.... Been there, done that, burned the tee shirt.

There are enough tried and true limb designs out there already that you can just look at and get pretty darn close to what you are wanting to build without having an engineering degree or using high tech software to do projected outcome. But even if you do the calcs, you will still need time and bows built to make subtle changes in wedge length, taper rates, tip wedges, type of material used, and on and on until you find the perfect combo. You change one thing at a time, test it thoroughly, and log the gains or losses.

Just moving the stops on your form an inch or so on a RC limb, can make a large difference.... Your tip notch location on the hook, just adjusting preload and limb pad angles make a huge difference too..... Why you are doing these small changes you are still making good shooting bows, and just logging the difference... You do this for a couple years, and your performance increases can be dramatic. it's called splitting hairs... you split enough of them, it turns into a pretty big pile of hair...

You see those construction site photos all the time where ya got Architects, engineers, project managers, superintendents, and owners all standing around the blue prints on a project. and there is always the guy standing in the center with a pencil behind his ear, with nail bags on, and sawdust in his hair telling all these guys why these plans are not going to work, and what needs to be changed to not only build it correctly, but often save a ton of money on materials doing it..... THAT is reality....   Kirk

[mmattockx]

Well we'll just have to agree to disagree on the engineering and air bow calcs being a necessary or even an important factor of building bows and testing different designs. The point i was trying to make is that you can do the super tiller calcs on the best energy storage and best limb shape to accomplish this, and once you actually build it , you find that it's vertically unstable and has floppy limbs.... Been there, done that, burned the tee shirt.

I agree it is not at all necessary. But it can be a tool that cuts development time and allows ideas to be examined without all the workshop time needed to build a bow just to find out it wasn't worthwhile.

There are enough tried and true limb designs out there already that you can just look at and get pretty darn close to what you are wanting to build without having an engineering degree or using high tech software to do projected outcome.

I would agree with that as well.

and there is always the guy standing in the center with a pencil behind his ear, with nail bags on, and sawdust in his hair telling all these guys why these plans are not going to work, and what needs to be changed to not only build it correctly, but often save a ton of money on materials doing it..... THAT is reality...

That's a poor engineer if he doesn't already know those things.


Mark

[Kirkll]

  I don't know whether i'd call them poor engineers, but there are a lot of engineers out there that way over build things to just cover their arse, and it can seriously effect the budget. I've battled  with architects and structural engineers for many years over this supervising large construction projects. Architects and engineers absolutely hate being questioned about their designs by the general contractor.... but you have to work with these guys closely, and choose your battles wisely.
Once a plan has been approved, the "Engineer of record" is the only one who can make changes... so it's a balancing act. 

I'm glad i'm done dealing with them in that capacity.   

Funny thing is.... If i could have gone to school longer, i honestly think i would have gone into engineering myself...