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Design v1: Walled Sides - Feedback welcome (weight bearing, cross bracing, design)

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Blog entry by PurpLev posted 02-07-2011 10:24 PM 3825 reads 0 times favorited 10 comments Add to Favorites Watch

I’m awaiting a benchtop milling machine which weighs about 500lbs, and with the expense of the machine + additional tooling that would probably follow (vises, cutters, tool holders, etc) I wanted to be able to minimize the expense on the stand.

most stands are in the 150-400 range (including shipping and such), which would be better used for other things. I still have some extra 4×4 FIR from building my workbench, and figured I might as well just use that. My first concept was the simple workbench/table style consisting of 2 sets of 2 pillars each connected with 2 2×4 using M&T. the 2 sets are then connected with 2×4 using unglued M&T with bed-style bolts to tighten the joinery and parts together (actually was leaning toward full length lead screws but it does the same thing):

the top is 1.5” thick and made of 2 layers of 3/4” plywood topped with 1/4” phenolic (for protection from liquids/oils/coolants/etc)

Thing is – I don’t really have much time to build this, and it’s too cold, icy, and grey these days for me to want to be in the garage. I wanted something that would take less work to put together.

I came up with the following design which consists of the following:
1. Uses 4 4×4 pillars to carry the weight that is put on the workbench
2. Uses Plywood to cross connect each 2 4×4. This would be the equivalent to the 2×4s and the M&T with the joinery basically being spread across the entire 4×4 faces
3. 3/4” plywood screws to the back of the 2 sets of ‘walls’ – this is so that I can easily break this down if needed while still maintaining a large surface contact between parts to generate holding power
4. 2 strips of 2” wide 3/4” plywood connect the 2 walls on the front – not for rigidity, but to keep the base square as it will house drawers with slides
5. top is again 2 3/4” plywood laminated together to ~1.5” thick top with 1/4” phenolic top layer to protect from liquids/coolants/oil spills.

This is not a complete model as I’m still missing the drawers, but before I commit to design I want to make sure I’m not missing anything in terms of strength and functionality of the base being what it should be – a strong base.

Feedback most welcome, especially from folks that have built stands to handle heavy weights. Am I missing anything? should I add more cross bracing anywhere? Any weak points? Anything else? Looks ok?

Thanks in Advance and Peace!

EDIT:
After considering the design and it’s ability to handle the required load and countering racking, and after calculating required materials and time to build the workbench, I decided that it was not worth it to build it as it will not save the expense, and will only add more work and time to build this bench up. I was able to find a stand on clearance that should handle the load (speced at 2200lbs) and decided to shut down this project.

Just putting this here, as sometimes projects do not go as planned, or do not make it past the design stage.. just an FYI, take it or leave it :)

-- ㊍ When in doubt - There is no doubt - Go the safer route.



10 comments so far

View JamesVavra's profile

JamesVavra

288 posts in 2070 days


#1 posted 02-07-2011 10:41 PM

Sharon – it doesn’t seem like there is much to keep that design from racking. I’d hate to see you bump into it from the side a bit too hard and send that 500# milling machine over sideways. Perhaps extending the front horizontal pieces the full width would help, but I’d still be more comfortable with the first design.

James

View HokieMojo's profile

HokieMojo

2103 posts in 2482 days


#2 posted 02-07-2011 10:55 PM

I think diagonal bracing can really help to prevent racking too, but I don’t have experience building suck large supports.

View JJohnston's profile

JJohnston

1602 posts in 2045 days


#3 posted 02-07-2011 11:11 PM

Does being a civil engineer licensed in 2 states qualify me? :D

Strength wise, you’re more than fine. Compressive stress from a 500 lb load on 4 4×4 legs (49 sq.in.) will only be a little more than 10 psi, which is nothing. You may want to keep the plan sized so the feet on the machine are close to directly over the legs, to keep bending stress in the top to a minimum.

Stability is the real battle, though, and JamesVavra is right: the open side is weak. The shear panels on the sides are fine (with 100% glued contact between them and the legs), though on the back, I’d be inclined to drill clear through and use bolts, with T-nuts in the legs (or better, part #90955A123 from McMaster.com). I also think you’re going to need to do this on both front and back, and just accept that you can’t have drawers.

If you have your heart set on drawers, the first design with the bed bolts will probably be OK, but I’d agree here too: widen the lower stretchers as much as possible, filling in the gap between the lower edge and the floor. You would also be wise to use a hard wood (not “hardwood”, but hard wood) because resisting racking will generate high compressive forces between the tenon shoulders along the edges of the stretchers and the legs.

-- "A man may conduct himself well in both adversity and good fortune, but if you want to test his character, give him power." - Abraham Lincoln

View PurpLev's profile

PurpLev

8476 posts in 2403 days


#4 posted 02-07-2011 11:18 PM

Thanks for the feedback, as far as compression I am pretty certain I’m over building this, and JJ you are correct, once I have the dimensions I’ll aim to have the legs as close as possible to being beneath the machine legs to avoid sagging of the top. The racking issue I was not so sure about and apparently for a reason… back to the drawing board.

-- ㊍ When in doubt - There is no doubt - Go the safer route.

View sIKE's profile

sIKE

1271 posts in 2508 days


#5 posted 02-07-2011 11:23 PM

Sharon,

Use the top design but for time sake, get rid of the MT use butt joints and use large lags(bedbolts)/glue (TiteBond III) for the joinery and then of course a Torsion box for the top…..it will be a tank…..

-- //FC - Round Rock, TX - "Experience is what you get just after you need it"

View sIKE's profile

sIKE

1271 posts in 2508 days


#6 posted 02-08-2011 12:36 AM

With a little more thought, I would change the joinery from Butt Joints to half-laps on the strechers. Glue and Screw and you will will have a very strong frame for your top.

-- //FC - Round Rock, TX - "Experience is what you get just after you need it"

View jlsmith5963's profile

jlsmith5963

297 posts in 2102 days


#7 posted 02-08-2011 01:53 AM

The down and dirty way is to treat the table as if it was rough framing. You can use Strong-Tie products, available at any Home depot, in conjunction with lag screws or through bolts.

You can even up grade to the black powder-coat line if you don’t want the galvanized finish.

-- criticism: the art of analyzing and evaluating the quality of an artistic work...

View PurpLev's profile

PurpLev

8476 posts in 2403 days


#8 posted 02-08-2011 02:38 AM

Thanks for the ideas. dealing with half laps and torsion boxes would be quite an ordeal – time wise. as for the half lap – it wouldn’t take me much more time to just do M&T since I’m already setting up machines for joinery which is what I’m trying to avoid.

As for the Strong-tie. this was on the design table and I was considering using these to connect 4×4 post with 2 2×4s on the corners:

I just don’t care much for the house-under-construction look that it presents so was trying to make it a bit more visually pleasing.

I am currently going to modify design #2 as posted in the original thread slightly based on a previous base that I made which was quite strong and had no tendency to rack, and will repost.

-- ㊍ When in doubt - There is no doubt - Go the safer route.

View Jon3's profile

Jon3

494 posts in 2859 days


#9 posted 02-08-2011 08:54 PM

Regarding the top: my G0619 at almost 500lb managed to flex a triple pky of 3/4” ply so much it scared me. I would laminate up a sold bench top if that is an option.

View PurpLev's profile

PurpLev

8476 posts in 2403 days


#10 posted 02-08-2011 08:57 PM

Thanks Jon, that is actually the Mill that will be mounted on the workbench. after calculating the necessary materials that I need and time estimated to build it, I decided to fork over the $150 and ordered a metal stand for it that is rated at 2200lbs.

Are you running the mill manually? or have you converted it to CNC?

-- ㊍ When in doubt - There is no doubt - Go the safer route.

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