Building a workbench

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Raymond Sanderson 2 on 21/06/2014 02:37:50:

Michael does this not greatly depend on the quality of plywood used, density of layers, so many factors these days to consider.

I must ask by double layer what thickness are you defining 30mm each or over all??

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Raymond,

Yes, of course, the materials are relevant, but [within reason] much less so than the shape.

The rule that "beam-stiffness is proproportional to the cube of thickness" presumes that the material is homogeneous and fault-free. … but, even in the Real World it is a good rule of thumb.

• Double the thickness and you increase the stiffness by eight
• Treble the thickness and you increase the stiffness by twenty-seven

The discussion started when Brian asked why he needed Glue and Screw his two boards together.

• When a beam bends, one skin is in compression and the other in tension and [to a large extent] the stuff in between serves only to (a) maintain the separation between them, and (b) prevent them from slipping relative to each other.
• This is how I-Beam girders work, and also those lightweight panels with honeycomb or foam cores.
• …. Nature's version is the internal structure of a Bird's bones.

If Brian is using 18mm plywood … Two sheets "loose layed" would only be twice the stiffness of one [because they can slip], but "fully bonded" they should act as a single sheet of 36mm, and be eight times stiffer. …

MichaelG.

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P.S. … Regarding foam-cored panels, etc.

Stiffness and Strength are not the same thing,

but it's often Stiffness vs Weight that's important.

[John McNamaraParticipant @johnmcnamara74883]

From memory. Beam deflection theory relies on the material being used within its elastic range of movement when a load is applied. The range where when the load is removed the beam reverts to it unloaded state. However if a load is applied for a longer time all material is subject to creep it will not return to its original position.
**LINK**

A bench used to support a machine while it may be strong enough is subject to creep, resulting in permanent deformation, in this case plywood may be more than strong enough to support the load, however if the machine is bolted directly to the wood, which is inclined to creep a lot, the accuracy of the machine might be compromised as it relies in a stable base to avoid twisting the bed.

If the bench has a metal frame can a couple of extra steel supports say channels be placed under the machine bolting down points. And maybe drill the table top and use some thick steel collars under the machine that will transfer the load through the table top directly to the steel supports?

Regards
John

[Brian JohnParticipant @brianjohn93961]

It is a lot easier to cut and fit timber ; you can ask the hardware store to cut it to size. It is not so easy to buy and cut metal.

Edited By Brian John on 21/06/2014 18:26:57

[Ian WelfordParticipant @ianwelford58739]

Just a thought but if you can try looking for someone who builds truck trailers bodies. They often use glass-fibre

reinforced ply and this stuff is really stable, heavy ( damping things well), comes in huge sheets ( and they often have offcuts ) and it bonds well. It's 20mm thick and usually has one "good face" of resin / laminate and another layer internally bonded in.

I've had some outside in all weather as a compost bin for 10 years now and the edges have started rotting but they're directly exposed to weather and untreated. Kept undercover it will outlast even marine ply!

Down side is you MUST WEAR A MASK when cutting this stuff and the damn dust makes you itch. Carbide saw blades are essential.

Ian

[Raymond Sanderson 2Participant @raymondsanderson2]

Michael & John both great insights into stress testing of materials, one of the topics I enjoyed doing during Mech Eng dip course wish health had not got in the way of me completing it.

Have a friend who does this for a living.

[Brian JohnParticipant @brianjohn93961]

Wow, that must be for a big lathe ! 

What is it ? Even at that thickness, it still bends.

 

 

Edited By Brian John on 22/06/2014 04:42:53

[Raymond Sanderson 2Participant @raymondsanderson2]

Posted by Brian John on 22/06/2014 04:40:56:

Wow, that must be for a big lathe !

What is it ? Even at that thickness, it still bends.

Edited By Brian John on 22/06/2014 04:42:53

Brian actually a test being done for a mine bridge with trucks loaded to 50t it broke at 48t I believe using the 200t jacks.

The fellow is close to retirement and is/will be buying a lathe as well as going into Model Engineering.

[Brian JohnParticipant @brianjohn93961]

I am a bit worried that this work bench will be too high at 130mm ? Is there some best height for these ? You can see from the photos that the side bars are set in the top holes ; the 18mm plywood is to be screwed onto the pine which is resting on the top in the photo. If I lower the height by moving the side bars down to the next set of holes, will the ends interfere with the operation of the lathe ? I do not think so but I am not sure.

 

 

 

Edited By Brian John on 23/06/2014 06:12:55

[Sam StonesParticipant @samstones42903]

Brian,

Are you suggesting that the bench uprights (legs) will be protruding above the surface of the bench? If so, they would present quite a working hazard.

I would choose to have the horizontal centre-line of the lathe at a height which allows my forearms to be horizontal while using the lathe. Of course, what you’ll be standing on comes into account too.

Regards,

Sam

[Sam StonesParticipant @samstones42903]

Brian,

From closer examination of your photographs, I would suggest that the left to right stiffness would benefit considerably from bolting a flat sheet of material across the entire back surface. That method avoids having diagonal braces running across otherwise useful storage space.

When I borrowed a small lathe, I had to stiffen up my existing (Bunnings) bench. Admittedly it was not as strong as yours.

I used 10mm MDF for the back and the ends. The difference was dramatic.

Regards,

Sam

[Raymond Sanderson 2Participant @raymondsanderson2]

Brian thats looks good in what you have planned, except I agree 1300 is going to be way to high unless your 6'5"+

Shame the sides can not be altered unless some cutting and welding takes place, I am sure the ones at Masters were only 850 high made by Amazon but look identical.

[Brian JohnParticipant @brianjohn93961]

I am not cutting anything off ; I did think about it but I fear that it might compromise the structural integrity of the frames. Not being an engineer, I am not keen to find out.

Yes, the bench uprights will protrude above the surface of the workbench if I lower the side frames to the next set of holes. But at this point I do not see any other solution.

[Keith LongParticipant @keithlong89920]

Brian

I've just measured my lathe on it's stand, and the spindle centre to floor is 125cm. I'm just about 6 ft tall and I built the stand so that I could use the lathe standing upright and not slightly stooping, as that plays hell with my lower back. Also it means that I can use a bar type stool/chair to sit on at the machine and still operate it comfortably. If you find the lathe too high on your stand, rather than lowering the lathe and having the bench uprights protrude, I suggest that you raise yourself on "duck-boards" to compensate, the softer feel of the boards will be kinder to legs and back and warmer in winter – though that might not be an issue on your side of the world.

Keith

[Ian S CParticipant @iansc]

In Sparey's book "The Amateur's Lathe, the height is found by standing upright against a wall with the arms extended downwards. Now bend the forearm upwards at the elbow and make a mark on the wall at the point where the bent elbow lies. It is at this height that the top surface of the topslide should be set.(also a good height for the bench vice).

For the bench he suggests 2 x 2 angle iron, or 3 x 3 wood, and 2" planks for the top,(he probably means a hard wood, not pine), how about Jara, or similar good Ausie hard wood, and you can machine it like steel, I know, I tried it when I was wood turning, one cut, sharpen chisel, boy it was hard work.

Stan Bray suggests the top should be moderately thick metal, or shuttering plywood, or block board, or even a couple of layers of thick chipboard. What ever wood is used , a layer of formica (or sheet metal) shold go on under the lathe.

If you make it an inch or two too high, you can use duck boards in front, but make it too low, and you'll have a sore back. Ian S C

[Brian JohnParticipant @brianjohn93961]

My initial idea was to use a slab of thick plywood across two very strong saw horses which are capable of supporting 400 KG. I thought that this might be too low but I am reconsidering as I could always sit at the lathe in a chair. Nothings says that you have to stand at the lathe.

[Raymond Sanderson 2Participant @raymondsanderson2]

Posted by Brian John on 23/06/2014 22:26:35:

My initial idea was to use a slab of thick plywood across two very strong saw horses which are capable of supporting 400 KG. I thought that this might be too low but I am reconsidering as I could always sit at the lathe in a chair. Nothings says that you have to stand at the lathe.

Brian these days I have no choice to sit at the lathe I am a wheelchair user BUT I use a Draughtsmans gas lift stool in my workshop with upgraded wheels and at full height. I do mostly wood turning using a Nova 300 a Jet Mini and the Myford ML7 along with other machines a metal & Wood Bandsaw, SCMS,

Yes everything I buy needs close attention as to MY use, I have the background to alter if need be not all the gear tho.

[Brian JohnParticipant @brianjohn93961]

Okay, so here it is with the lowered height : work surface is 98 cm high. The frames are still not quite square which really puzzles me. The only way this could happen is if the side beams were different lengths but they are not. Anyway, that does not affect anything and I do not think the cross beams on the ends of the frames will interfere with the operation of the lathe.

 

 

Edited By Brian John on 24/06/2014 06:07:33

[Raymond Sanderson 2Participant @raymondsanderson2]

Brian have you measured diagonals of each end frame. Corner to Corner both ways this will give an idea IF the frame is out of square measuring length doesn't.

It could then be floor deviation or the pressed clip in area for the cross bearers. Wedges or floor jacks (a nut and bolt each corner to adjust twist of the table/bed.

If its the table only out then packing/shims under it can help.

I know the lathe you have is small but what length difference is there?

Its almost worth buying the tube, cut it to size weld it up and be done with it.

[Brian JohnParticipant @brianjohn93961]

I have measured the diagonals and they are equal in all respects. I have called Bunnings and they said to bring it all back in and they will have a look at it and exchange it if necessary. I may do that on Friday.

[Oompa LumpaParticipant @oompalumpa34302]

Posted by Brian John on 24/06/2014 05:49:34:

Anyway, that does not affect anything and I do not think the cross beams on the ends of the frames will interfere with the operation of the lathe.

Edited By Brian John on 24/06/2014 06:07:33

You are going to regret this. You are going to put a lathe on the top of the stand, in the face of all of the advice from some very experienced people, put some stock in the chuck and turn it using thousandths of an inch as the measurement? Surely you can take a tape measure and a saw (any saw, doesn't matter – except wood won't work) and cut six inches (or whatever) off the top of the stand's legs and get some plywood and make some proper ends for it. It's the sort of job many on here would do on their way past into the workshop in the morning. While your'e at it, put a back on it and make some decent storage space.

What you have right now is impractical, ugly and frankly, not fit for purpose. Grasp the nettle with both hands and go for it. If you want, PM me your 'phone number and I will give you a call and talk you through the basic steps. It's not hard and much simpler than some of the tasks you are about to embark upon with the lathe the stand is intended for.

Just my opinion having fixed more than my fair share of bodge jobs in the past.
graham.

[BazyleParticipant @bazyle]

Good to see you are setting up in the dining room. Saves time coming in for meals and if the wife forgot to warm up the custard you can run another screwcutting pass between courses.

Lathes end up too low because advice from old books (and blokes) forgets that each generation is taller. As Keith said earlier you can always stand on something.. I suggest you take your watch off and adjust the time. As you do this note where you are holding it to see clearly and use your fingers which will be the level you want the chuck centre to avoid getting a sore back.

[Gordon WParticipant @gordonw]

My lathe is 47" high at center hight, this is the same as my elbow hight, often said to be the best setting. It is too low ! get a bad back very quickly. I would follow the advice- set it higher than you think and use duck boards if needed. I am 6'-2" tall but short legs.

[Brian JohnParticipant @brianjohn93961]

If the bench is too low then sit down ! Is there some reason that you have to stand up to use a lathe ?

The most that could be cut off the top is 2 inches. There is a horizontal beam on the ends at that point as you can see in the photos. It is welded on and cannot be moved.

There is need for any backing. This whole system is rock solid and it does not move, wobble or wiggle in any way at all. All other so called ''workbenches'' sold at the hardware stores would move all over the place when nudged with one hand !

The top will be 18mm, 7 layer plywood which will also be screwed to 19mm pine boards to increase stiffness and strength ie. a total of 37mm thickness.

I am hoping to look at the Masters Hardware version today ; perhaps it is lower in height.

[Brian JohnParticipant @brianjohn93961]

UPDATE : the Masters Hardware  version (Amazon) is the same height so no luck there.

Edited By Brian John on 25/06/2014 09:25:09

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Bazyle on 24/06/2014 13:10:09:

… I suggest you take your watch off and adjust the time. As you do this note where you are holding it to see clearly and use your fingers which will be the level you want the chuck centre to avoid getting a sore back.

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Bazyle,

That is some of the best, and most concise, advice I have seen.

MichaelG.

[Ergononomics at Loughborough 1968-71]

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