Size bolts required? 8020

[adam_m]

When bolting 1/4" steel to 8020 - 2020 what size bolts should I order? Is there a recommended number to use per foot?

Thanks.

Adam,

[adam_m]

No one has bolted 1/4" steel to 8020?

[rschieck]

If you are using fractional Inch 80/20 then the slots will take the head of a 5/16" carriage bolts. IIRC I use 3/4" long ones to put the steel on to my 3030 80/20.

hth

Rob

[Aryantes]

Not many people use 10 series 8020. ( I assume you aren't using metric 2020 as that would be extremely small for a gantry support. )

If you want to use 2020, you'll have to find a carriage bolt with a square neck that is going to fit properly.

The slot in 2020 is 0.255" wide.

The neck on a 5/16 carriage bolt is 0.322" wide and would not fit in the slot. (Taken from McMaster)

1/4-20 carriage bolts are also too wide, 0.260"

#10-24 bolts are 0.199" and will fit. 0.199 * square root of 2 = 0.288" which is the width of the diagonal.

In this case, it 'should' work and the neck shouldn't rotate in the slot.

Its not as nice a fit as 5/16 bolts into 15 series 8020.

I haven't tried it though.

You should use as many bolts as you can really. They are really cheap. Just drill as many holes as you can before it starts looking ugly. hehe.

[adam_m]

yeah, like an idiot I bought some 2020 to use with some 1/4 x 8" CRS... My plan is to use two lengths to support the steel in a 60" - 65" length.

What do you guys think?

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Adam,

[jscavitto]

I did something similar 2040 with 1/4 crs on it.

I used the econo tnuts from 80/20 and 1/4-20 5/8 cap with a washer and lock washer to attach mine

[adam_m]

I'm wondering about strength, stability and deflection...

Will the (2) - 2" x 2" be enough to take any deflection on a 6' foot span?

Adam,

[jscavitto]

you should look at the 80/20 deflection calculator however it won't account for the crs.


Assuming a single beam accoss that is supported on each end and a center load of 30 pounds you will deflect .049 at the center of the 2020 span.

If you attach the steel you are NOT going to see that amount.

[adam_m]

So, how do I account for the force of the load? Is that determined by what I'm cutting and at what speeds I'm cutting at?

Assuming I'm using double the amount of 2020 does that half the deflection amount?

I tried the calculator and assumed a 2040 and the deflection of 30lbs on a 72" span would be .009 and at 100lbs. its only .024, strong stuff!! Is that realistic that if I'm doubling my material that I can use 2040?

Thanks,

[jsheerin]

No, you can't use 2040 to be equivalent to two pieces of 2020. Yes, using two pieces of 2020 will reduce your deflection by half (at least). How the pieces are connected together will effect what the deflection is. If you stack the two pieces of 2020 but only attach them at the middle and the end, then the deflection for a given load would be half what it would be with one piece of 2020. This is because the two pieces of 2020 can move in relation to each other (slide across the mating surfaces). If you have a solid piece of 2040, the piece can't slide at that location which is where shear stress is highest, so it reduces deflection by a much larger amount. Beam deflection is typically reduced by the third power of the height of a beam, so if you double the height of a solid beam, deflection will be reduced by 8 times (2^3).

Now if you attach the two pieces of 2020 to a piece of 1/4" CRS using an appropriate bolt pattern, then the stiffness will be increased more than just using the two pieces of 2020 stacked. That can be calculated, but it is a bit trickier to do.

A typically assumed cutting load around here is 50 pounds. You just have to know what it is and design your frame for a desired amount of deflection. The problem is that no one really knows what the cutting forces we see on our types of machines are. I plan on trying to take some force measurements before building my next router to get a better idea.

[adam_m]

Thanks for the informative post jsheerin. I will be using 1/4" x 8" crs appx. 6' length.

...using an appropriate bolt pattern.

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What would the acceptable bolt pattern be for the above design?

Adam,

[jsheerin]

I remember doing the calculations for bolt spacing in school, but it's been too long. I would space them closer than 8" for a good start.

However looking at the dimensions on the 2020, I'm not sure how well this will work for you. What are you using this assembly for? I used a 7" wide piece of 1/4" CRS on the gantry of my router. It had a bow in one edge. I had to pull it flat against the piece of 3060 I had it attached to using the attachment bolts. I'm thinking the 2020 might not fare so well in a similar situation...