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Old 01-10-2014, 11:02 AM
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traveller (Bo)
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Need some advice on pier

Yes, finally heading down the pier path... (also taking inspiration from Meru's pier build http://www.iceinspace.com.au/forum/s...d.php?t=114718)
I have a pier with the following dimensions
250mm round top plate, 250mm square bottom plate (both with pre-drilled holes)
100x100mm square, 900mm high and 6mm thick steel.
I plan to mount my EQ6 head on it.
I have the following questions for experience pier builders out there:
1. Do I need to weld a heavier bottom plate to my existing bottom plate? I was thinking of a 350mm square plate of 10mm thick.
2. Gusseting: I plan to put two gussets on each side. The pier will then be secured with four bolts between the two gussets and then four more at the outer corners of the new base plate (see my sketch). The bolts will be poured into the concrete base (450x450x600 (d) with reo)
3. Top plate. I am thinking of a new 250mm round top plate 6mm thick (same dimension as my existing) and attach the two via 4 thick threaded rods (is that a "rat cage"?) and then make an EQ6 adapter.
Any comments on my proposal is very much appreciated.
Bo
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Old 01-10-2014, 01:09 PM
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Bo, what you are planing to do to the pier to strengthen it is fine, but remember a pier is only as stable as the foundation it is fixed to.
If your concrete is solid and can handle some serious Dyna Bolts all should be well, however if thin and weak you will lose your stability.
Not trying to put you off here, but it is all about foundation, in the ground or above.

Leon
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Old 02-10-2014, 10:14 AM
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traveller (Bo)
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Thanks Leon,
If stability is the key, then would I be better off with a wider base than depth, so instead of 450x450x600 (wxbxd), would I be better off with 600x600x450 (wxbxd)?
Cheers
Bo
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Old 02-10-2014, 10:37 AM
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Perimeter welding a thicker plate to the existing thin plate won't do much to strengthen it, you are better to cut off the thin plate and weld the pier directly to a 10mm thick plate, then add corner gussets that are at least 400mm long.
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Old 02-10-2014, 10:59 AM
Roger273 (Roger)
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Hi Bo
After I had finished the slab for my pier I had an idea that I should have used to make it more stable. Instead of just a square hole, flair it out a bit towards the bottom to give it a wider base (I live on a flood plain so very soft alluvial soil). Too late for me now but if your soil is soft might be worthwhile.

Another idea, instead of dyna bolts, I used threaded rod and inserted it into the wet concrete after I had finished the pour. I used a plywood template with the hole layout I wanted, and a rod through each hole with a nut above to give me the height I wanted (no nut underneath the ply). The threaded rod was bent a little towards the bottom so it couldn't turn once the concrete had set. Place the structure on the wet concrete and push the bolts down to sink them into the concrete, with plenty of up and down movements to expel any air and bed them in well. Worked a treat!
Cheers, Roger
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Old 02-10-2014, 11:06 AM
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Bo, if the concrete you are fixing it to is stable, than what you have will probably suffice, and a larger plate would not make that much difference.

It is like fixing a Bull Bar to a car, it, the bull bar could handle a bull, but if only fixed to the car by a couple of bolts would be useless and break off at the fist bump.

I think your pier will be fine if the foundation concrete is solid, just go with it, you may be pleasantly surprised.

Once fixed to the concrete, is there anyway of filling the pier with sand, right to the top, this helps with vibrations to settle quickly.

Leon
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Old 02-10-2014, 11:11 AM
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Thanks Roger,
I plan to cast long threaded rods into the concrete (pre-bent) as you suggested. I live in an area with very solid clay soil (there used to be brickworks all over the place in the 1900s and large clay pits in the ground, they have since been filled and council has created many parks on top of them).
Matt, thanks for the advice re taking off the thin plate and re-weld a 10mm plate. Just checking I will need 400mm long gussets, a slight overkill given the load capacity of an EQ6?
Bo
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Old 02-10-2014, 11:15 AM
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Thanks Leon,
Yes, I see what you mean now. Given I live on pretty solid clay soil, I will go with my original 450x450x600 footing. I will gusset up the existing plate without welding a new plate. There is a 12mm hole on either end of the pier, so I will need a bit of time to fill her up with sand
Bo
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Old 02-10-2014, 02:16 PM
Kunama
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With regard to the top plate, consider its size only needs to be big enough for the mount, too big a plate may foul the mount/counterweights etc.
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Old 02-10-2014, 05:11 PM
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Don't use a top plate on top of threaded bolts. These are totally unnecessary. You can polar align with a slightly out of level top plate. The use of such bolts can give rise to a point at which flexure can occur.
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Old 03-10-2014, 09:14 AM
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Quote:
Originally Posted by Paul Haese View Post
Don't use a top plate on top of threaded bolts. These are totally unnecessary. You can polar align with a slightly out of level top plate. The use of such bolts can give rise to a point at which flexure can occur.
Thanks Paul and Matt,
So I can safely trim the 205mm top plate down to around 150mm and then bolt the EQ6 adapter directly to the top plate?
Bo
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Old 03-10-2014, 09:56 AM
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koputai (Jason)
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Quote:
Don't use a top plate on top of threaded bolts. These are totally unnecessary.
I'm glad I'm not the only one who thinks this way. I brought this up a few years ago, but no one would agree with me!

http://www.iceinspace.com.au/forum/s...ad.php?t=76881

Cheers,
Jason.
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Old 03-10-2014, 09:57 AM
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Put another plate on the top and the bottom if both are under 10mm. Weld another plate to the existing if you like.
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Old 03-10-2014, 10:06 AM
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Got it, thanks guys.
This is the latest design:
Remove 6mm top and bottom plates, reweld a 250x250x10mm plate to bottom and a 150mm diameter 10mm plate on top. Gusset up the bottom plate (6mm or 10mm?)
Machine an EQ6 adapter and bolt directly to the 10mm top plate.
Bo
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Old 03-10-2014, 10:06 AM
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koputai (Jason)
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Quote:
So I can safely trim the 205mm top plate down to around 150mm and then bolt the EQ6 adapter directly to the top plate?
Yes you can, no drama, and as said it will lessen the likelihood of any fouling. That said, my pier has a 300mm square (16mm thick) top plate with an EQ6 adapter bolted into the middle. I did this because I have dreams of a bigger mount one day. At the moment, the extra real estate is great for sitting eyepieces whilst viewing!

Cheers,
Jason.

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