Building a flex tester

[skialex]

Hi Ballers, I'm building a flex tester. I'm trying to keep the cost low and so far I have gathered the components from stuff that I already have, the only thing I needed to buy was the scale. So far so good I'm ready to build the cage.

I'm using heavy duty press formed steel and an aluminium rod which I already had and I will weld the pieces in my work shop. It will be a little on the heavy side but it's free and it doesn’t flex under pressure.

I have read all the posts regarding flex testers on BOS and elsewhere and I have a question. I know that from one side to the middle where the depth gauge sits should be no more than 17" in order to be able to take the tail measurement, so how long the cage should be, 34"? Is it a bit unsafe to place the end of the tail against the cage, should it be better if it is a little shorter and how much shorter? Is there a standard length?

If interested, I will take pictures and post them when I'm done.

Thanks you,

Alex,

 

[AdamCord]

@skialex the "standard" width for a flex tester is 24" from cross bar to cross bar, and the jack goes in the middle (12" from the ends).

[skialex]

Thank you @AdamCord now I can cut the pieces!

Thanks again!

[A_B]

Look at the special notched out bar that allows flex to be tested without removing the fin. I wish I had one on mine.

 

[A_B]

 

[Bruce_Butterfield]

Normally you remove the fin for the 17" measurement. One thing I do is also measure at 20" so if I suspect a ski is getting soft I can check the tail without removing the fin.

 

Pretty slick idea with the notch though.

[skialex]

@A_B I know, I have seen the pictures, I will try to make the cut out bar for the fin but I would probably have to pay someone to fabricate it for me, so I'm thinking that if I can not make a solid one myself I will leave it as an upgrade option. Thank you.

[A_B]

Another idea for the notch out.

 

 

[mwetskier]

almost certainly the tail flex number will differ some what with or with out the fin block attached -though that slight deviation might not matter much. maybe all skis are always tested with the block in place but i think that might be a question to ask some one with knowledge of such things.

[A_B]

Easy enough to try both ways and see any difference. But after you establish a baseline with or without, then just test it the same way and you will see if there has been a change. Which is what you are looking for after you record initial flex and you keep the ski.

[skialex]

 

Not ready yet, not even half way but I'm getting there.

I managed to test it though, numbers look right and the frame is rigid.

[skialex]

I still have to reinforce the welds, ad cross bars for the scale to sit on, cut off the excess metal from the scale, make a base for the digital display, fabricate a base for the depth gauge.

I also have to reinforce the rear round cross bar in order to make a slot for the fin.

Finally I will sand it, puttied it an sprayed it.

 

[bishop8950]

Very nice. One thing to consider is the flex numbers will be different if the bars at 24" are on rollers or not. I can't rember how much, but I heard this was an issue when comparing numbers in the past.

[bishop8950]

Very nice. One thing to consider is the flex numbers will be different if the bars at 24" are on rollers or not. I can't rember how much, but I heard this was an issue when comparing numbers in the past.

[skialex]

@bishop8950 thanks, do you suggest that the bars should be on rollers, is that the industry standard? The only picture I have seen that the bars can roll is the yellow flex tester that Schnitz used to sell.

 

[skialex]

@bishop8950 thanks, do you suggest that the bars should be on rollers, is that the industry standard? The only picture I have seen that the bars can roll is the yellow flex tester that Schnitz used to sell.

 

[DW]

@skialex: The rollers will or should reduce the hysteresis or "sticktion" when measuring the flex of the ski, somebody can probably give an idea of how much they have seen from their own experience. I poor man's substitute might be something like wax paper between ski and bar. For no other reason than true accuracy, rollers should be the industry standard, although I doubt there is one as it is a pretty small circle.

 

What would be really cool, would be to incorporate not only vertical flex, but the ability to measure torsional flex in one frame or piece of equipment.

 

[DW]

@skialex: The rollers will or should reduce the hysteresis or "sticktion" when measuring the flex of the ski, somebody can probably give an idea of how much they have seen from their own experience. I poor man's substitute might be something like wax paper between ski and bar. For no other reason than true accuracy, rollers should be the industry standard, although I doubt there is one as it is a pretty small circle.

 

What would be really cool, would be to incorporate not only vertical flex, but the ability to measure torsional flex in one frame or piece of equipment.

 

[skialex]

@DW I'm thinking of how to make a poor man's substitute, so far I have thought of using a sheet of very thin stainless steel that I already have, make small cuts on bars and add some pins to help the curved pieces to roll freely under pressure around them.

Any ideas are very welcomed

[skialex]

@DW I'm thinking of how to make a poor man's substitute, so far I have thought of using a sheet of very thin stainless steel that I already have, make small cuts on bars and add some pins to help the curved pieces to roll freely under pressure around them.

Any ideas are very welcomed

[skialex]

Something like this, 0.5mm very easy to bend

[skialex]

Something like this, 0.5mm very easy to bend

[DW]

Another option might be simply leave the ss flat and put some grease / lubricant between it and the bar (so the ski stays untouched)

[DW]

Another option might be simply leave the ss flat and put some grease / lubricant between it and the bar (so the ski stays untouched)

[skialex]

@DW Thanks, I thought of that too, to put grease between the ss and the bar, it might work, I'll try it and I'll tel you how it went

[skialex]

@DW Thanks, I thought of that too, to put grease between the ss and the bar, it might work, I'll try it and I'll tel you how it went

[bishop8950]

@skiex I am not aware of any industry standards. But the machines I have seen do have rollers. I am guessing we would want to have precision of +/- 1lb if we are comparing the same ski with two machines. But if you are just tracking your own ski over time I am sure non rolling bars will be close enough. Lastly, putting grease on a ski sounds like a bad idea. Instead just get some calibration of the difference between machines. Maybe it's "I take xlbs off of my numbers to closely approximate roller numbers". I bet it's no more than a few lbs difference.

[bishop8950]

@skiex I am not aware of any industry standards. But the machines I have seen do have rollers. I am guessing we would want to have precision of +/- 1lb if we are comparing the same ski with two machines. But if you are just tracking your own ski over time I am sure non rolling bars will be close enough. Lastly, putting grease on a ski sounds like a bad idea. Instead just get some calibration of the difference between machines. Maybe it's "I take xlbs off of my numbers to closely approximate roller numbers". I bet it's no more than a few lbs difference.

[skialex]

@bishop8950 thank you. I mostly want to track skis over time. I would never put grease or anything slippery on the bottom of a ski, I would not even touch it with sweaty fingers :) I meant to put grease between the round bar and the wrapp around stainless steel sheet to make it act as a rolling bar.

[skialex]

@bishop8950 thank you. I mostly want to track skis over time. I would never put grease or anything slippery on the bottom of a ski, I would not even touch it with sweaty fingers :) I meant to put grease between the round bar and the wrapp around stainless steel sheet to make it act as a rolling bar.

[skialex]

 

@A_B notch out reinforcer ready to be welded on the cross bar, it took me 20min to cut it with an angle grinder and another hour to do the edges and make look nice.

[thager]

Rollers for a flex of 1/10 of an inch? Might be a bit of overkill if you ask me. Nice job @skialex! Might also be able to sell those to MC for rudder fin fixs!

[skialex]

Dial indicator arrived today!

 

[skialex]

Almost finished, I have a minor wire issue with the display which I'll have it fixed in the next couple of days !

[JayG80]

Nice work Alex. In addition to the flex tester, you may make a square to measure the flex points from the ski tail.

 

1/2" x 1/16" aluminum flat bar and hack saw scribe marks at 17", 25", 33" & 41"

[skialex]

Got it @JayG80, I have a metallic retractable measure that is wide enough and does not retracts because it's broken. I'm cutting it at 43-44", cut a slot for the fin and drill holes at the center of each flex point No.

Thanks, it's a very good idea, if it doesn't work I'll make the aluminum flat Barr that you suggested, or a wooden on that tailors use.

Thanks again

Alex.

[skialex]

@JayG80 this is the measure with the slot and small holes at 17"25"33"41" so I can mark the ski with a pencil.

Or make slightly bigger holes for the dial indicator and leave the measure on while testing the ski, in that case I would not need to use a pencil.

 

[Stathis Ventouris]

Nice, can't wait to see the results!

[A_B]

I found a wireless scale for mine if you want another option, although you already have a scale.

 

I put a small dot on my skis, as you need to get as close to possible in the exact same spot each time. Off a few mm's may yield a slight variance.

[skialex]

@A_B thanks for your suggestions, I live in Greece and it is impossible to find a scale that measures in Pounds, so I bought a scale that measures in Kgr and put a value of 2.2 which is as close to Pounds as it could get. Then while I was putting brackets to the display unit I messed with a circuit board and I had to give it to a friend to fix it. At the same time I found another scale in the UK that measures in Pounds, the price including shipping was not that bad so I bought that too.

Now I wait for the display or the new scale, whichever comes first.

Shipping and sometimes customs makes it impossible to buy stuff from the U.S.

For the dial indicator I paid $23 for shipping and it took almost a month to arrive.

The dot thing is a great idea, I'll use it too!

@Stathis Ventouris I think that this weekend we will flex test our skis, but after skiing, the weather forecast looks very promising for next weekend!

[skialex]

My flex tester is finally completed. So I measured two new skies that I had the factory numbers and I think that my numbers are quite close to the factory's.

HO V-type, my numbers were about 0.5lb higher than factory but I did not write them down and I gave the ski back.

Radar Vapor, got 1- 1.5lbs difference but I left the ski on at the 41" for few minutes to answer my phone and the number drop to almost the factory number.

Vapor Factory: 78 98 120 138

Vapor Skialex's: 79.42 99.46 122.96 138.38.

 

[skialex]

@AdamCord, @A_B, @bishop8950, @thager, @DW, @JayG80, @Bruce_Butterfield thank you very much for your advice and suggestions.

Also could anyone tell me what the preloads for Goode and Maple ski are? I’ve got the preloads for other manufacturers from a @MattP’s post.

@AdamCord do I take the number after few seconds or do I wait maybe few minutes until I'm 100% sure that the scale's number would not go down any more?

 

[skialex]

 

[A_B]

Me and a friend who has a fancy high priced flexer tested varying pre loads and I believe the results were it didn't matter. You can try yourself easy enough to confirm. The ski just needs some amount of stress.

 

We did this year's ago, so my memory could be erased at this point!

[AdamCord]

@skialex nice flex tester!

 

Mapple usually preloaded to around 40. I'm not sure about Goode. It's true that the amount of preload doesn't make a huge difference on the final numbers thanks to Hooke's Law, F=kX. So long as you are in the elastic deformation range (preload isn't super high), the final flex number will be close. All that really means is that if you know you want to preload to 40 and you hit 38 or 42 you don't really have to worry about getting any more accurate than that.

 

Normally we select the highest number seen on the scale. Keep in mind that when skiing the ski flexes and unloads in a very short amount of time so it doesn't have time to creep. If you are seeing a lot of creep though it could be a sign that the tester has some flex in it, or more likely that the ski you are flexing is seeing elastic creep. Some amount of creep will always be present but if it seems like there is a lot (dropping by more than a pound) it's likely that your ski either (A) was never fully cured or (B) was built using an inferior resin system.

[skialex]

Thank you @AdamCord, @A_B, I will test some more skis that factory numbers are available to me in order to compare and up my level of confidence.

The Vtype numbers were really close, I have to measure it again and write them down.

I also repeated the process for each ski and I came out with the same numbers, so I believe repeatability would not be an issue.

I personally ride a Goode and if anyone can help, I still would like to know what the factory preload is even if it does not make much difference only just to increase accuracy.

Thanks Alex,

 

[A_B]

I think Goode was 60. I built my tester when I was riding a 9500 and believe I was told to use 60. Again, we tested a range of pre loads and did not see any significance. If I remember right, we loaded at 10-80 pounds.

And points in between. The bounce, which is when you first get the deflection and what it settled on after several seconds was something we were looking at for recovery or rigidity, but never proofed anything with it. Just watch your scale weight at initial .001 deflection and then what it settles in at. We deemed that recovery, some had wider ranges than others. Less range and we thought that could indicate springiness of a ski responding back to original shape after load. All theory though.

[skialex]

Great info @A_B , very helpful, thanks!