What type of screw for worksurface hold down?

[Andrew TinsleyParticipant @andrewtinsley63637]

I have some thick worksurface material about 45mm thick. I want to screw it down onto a 2″ square tubular framework. For neatness I would like to screw into the bottom of the worksurface. What type of screw is most suitable. The worksurface is compressed wood particulate , which I assume has some bonding material mixed with it.

I have zero experience working with this type of material and would assume a fairly coarse thread would be needed. It would not surprise me if there are special screws for the job. Can anyone enlighten me?

Thanks,

Andrew.

[Roderick JenkinsParticipant @roderickjenkins93242]

I’d be inclined to use insert nuts in the work surface and a suitable machine screw through the frame.

Insert nuts from screwfix

 

Rod

[egaParticipant @ega]

There may well be special screws but any of the usual modern variety will serve. You could use CA glue on the threads to improve grip. These screws are intended to be driven without pilot or clearance hole but are inclined to throw up a burr at the entry point which you may need to provide for.

Have a look on the Screwfix website.

[Nigel Graham 2Participant @nigelgraham2]

There are screws made to be suitable for such materials – perusing a building-trade catalogue (e.g., Toolstation or Screwfix) may guide you.

The screws may well need a suitable pilot hole of diameter equal to of a shade larger than, the core of the thread.

You don’t normally need measure these accurately if the box label does not specify it – judging them holding the drill and screw up next to each other in line against the light, to see how much of which is eclipsed by the other is enough.

It would be worth experimenting in an off-cut.

[Mark EasingwoodParticipant @markeasingwood33578]

Hello,

Guessing you mean chipboard or MDF, then any of the commonly available modern plated screws should be ok for using in the face of particle board. They are generally hardened twin thread, and waxed these days, you can even use them as self-tappers when needs must! A thicker gauge and pilot hole may give the best result.

The more specialist “HiLo” or “Carcass” screws are meant for use in the edges, as are “Confirmat” screws, all these types are usually only available in a couple of lengths though.

Mark.

[VicParticipant @vic]

I’m not exactly sure what type of material you have, but out of interest I have some 15mm bench top material called Trespa and find it takes a good thread, at least in M6 when I’ve done it. Trespa is I think compressed paper and Resin? I’ve got a Nutsert tool so I’d probably use that if it didn’t take a thread directly.

Edit: This is the stuff I have. https://www.trespa.com/en_US/Trespa-toplab

[Master of noneParticipant @masterofnone]

I agree with using wood screws but I think you get a stronger fixing with a single thread.

[BazyleParticipant @bazyle]

Gosh, everyone on here is just a metal worker? Traditional woodscrews are tapered along their length but for particle boards they invented parallel screws decades ago generally known as ‘chipboard screws’ also characterised by having a deeper thread because of the weakness of the material. More recently, the last decade, just about all screws used in the building trade became coarse parallel threaded so most likely any new screw you buy will be of that type.

[Paul LousickParticipant @paullousick59116]

I’m assuming the bench top is made from particle board as used on commercial desk furniture. Therefore use particle board screws, available from your local hardware store.

The main difference between woodscrews and chipboard screws lies in the threads which, on a chipboard screw, run all the way along the screw’s length to the underside of the head. One notable difference is that their grooves are typically asymmetrical to allow for better resistance against pull-out. They also usually have thinner shafts that enable installers to screw them into the necessary materials more efficiently than regular screws.

Drill a clearance hole thru the steel frame and a pilot hole in the bench top, slightly smaller than the minor diameter of the screws.

[HopperParticipant @hopper]

I use roofing screws for such work, the ones designed to go into wooden trusses, not metal. They are a high(ish) tensile 6mm diameter coarse parallel thread with a flanged hex head so you can drive them in hard with a cordless drill with hex driver socket with a magnet in it to hold the screw while getting it started, made for the job and available wherever screws are sold usually. They hold sheet iron on the roof in cyclones around here so you won’t move a benchtop held down by them.

[JasonBModerator @jasonb]

Most chipbpoard or “carcase” screws will not be long enough to go through your 50mm timber and then into the worktop enough. I can get through a few 1000 a year but that is joining 18mm material to other chipboard. They are also designed to go into the side of the board not the face.

Screwfix Turbo will do the job as will Toolstations Screw-tite or Screwfix Goldscrew if you prefer Pozi head. In both cases I would suggest drilling 5mm clearance holes in the framing so the screw pulls the worktop up tight and there is no risk of jacking. No predrilling of the worktop.

[Clive FosterParticipant @clivefoster55965]

+1 for the insert nuts suggested by Roderick. Discovered those a few years back and find the much more predictable than wood or (so called) chipboard screws. Bit of glue helps lubricate things and makes for tight hold.

Lots of superficially similar wood screw / self tapping style screw out there. There is a reason for the multitude of types. Somewhere I have a PDF exiling the differences and why they are important.

As I recall things it’s all about getting stability of the shank so it pulls in straight and doesn’t wobble under side loads. Apparently the pilot hole size is important. The modern fashion for banging a single thread screw straight in is not good practice for strongest results.

Quality of the common import screws from the big box stores is generally pretty “meh” and dropping anyway. 20 ish years back when I was putting up and furnishing my workshop I ordered boxes of just about every size of screw I thought I’d need from the Screwfix Gold range. Screwfix seem to have changed the design / source at least 4 time since. The latest versions of the sizes I regularly use are noticeably inferior to the part box hangovers from the first batch.

Clive

[JasonBModerator @jasonb]

I don’t think I have ever seen kitchen or bathroom worktops held down with inserts, always a csk screw through the front rails and small pan head at the back which generally uses angle brackets on flatpack or solid carcases will tend to be same as the front fixing. Carcases will give up long before the screw pulls out of the worktop.

Was talking about some roof structure modifications with the Structural engineer I usually empoy a few months ago and when I asked if he wanted bolted connections he said No, Timberlok screws will do and that he seldom specifies bolts and timber connector washers between these days. So that is what was used, driven straight in with impact driver and no pilot hole, the plain shank allows the thread in the second timber to be pulled up tight.

[Andrew TinsleyParticipant @andrewtinsley63637]

Hi Jason,

The framing for this bench is steel not timber. It is approx 2″ square . Three sides are flat and the forth has a groove to take special joiner nuts, The long sides of the frame have the slot at the bottom and the two sides have the slot on a vertical edge.

The frame is heavy and on castors which can screw up to leave a solid mounting to the floor. If I ever want to lift the bench, it would be by grabbing the end of the bench, which protrude from the frame. I suspect normal woodscrews may well just pull out when treated thus!

Andrew.

P.S. There seems to be little agreement between contributors to this thread, so I am just as confused as when I asked the question in the first place!

[JasonBModerator @jasonb]

Sounds like Unistrut to me

Here you go bit of Unistrut screwed to an offcut of 40mm worktop. Angleplate and G clamp holding a 56lbs anvil to it.

just the ONE 5 x 60 screw screw with a spacer so about 35mm into the worktop.

 

 

I assume you will use more than one screw in which case unless your frame is bolted to the floor when you try to lift by the worktop it should stay attached. I suppose the differences are from those of us that work with wood for a living and those that don’t. Same people who said the stand for my CNC was no good yet now several years since and a lot of work done with the machine and no problems with the screwed together stand. Mark, Ega and myself have said modern woodscrews will do, we work with wood.

 

 

 

 

 

[HOWARDTParticipant @howardt]

If you are going to use the work surface for any heavy duty work either screw some tapped plates to the underside and  attach with bolts from below or simply bolt through from above and plug the holes.

[Andrew TinsleyParticipant @andrewtinsley63637]

Thanks Jason,

It may well be that the material is Unistrut. Certainly looks as if it could be from your photos. I don’t work with wood if I can help it, hence my query in the first place.

Howard,

I intend to use the bench for mounting heavy equipment. I have to admit that the use of bolts is very appealing!

Andrew.

[JasonBModerator @jasonb]

“Holding down” the worktop and supporting heavy machines do not actually require the fixing method to transmit any load as it is all downwards. It is only your subsequent wish to lift the bench by the worktop that needs something to stop them coming apart.

I thought your requirement from the first post was to avoid fixing by bolt, screw or whatever from the top now you want to bolt it to plates? The bolts will add nothing in compression which is where heavy machine loads will be acting on it.

I have a mill, bench drill, two grinders a linisher and a few other limps of iron on a 30mm kitchen worktop all held to to what is below with 4mm woodscrews.

[JasonBModerator @jasonb]

Coming back to pull out loads etc, it’s a long time since I have done strauctural calculations so better to just use a practical approach

The first post and subsequent reply relate to holding the worktop down to the frame and then being able to lift the frame by the worktop.

Holding the top down to the frame really puts no load on teh screw save for resisting a bit of possible cupping

Lifting the frame by the worktop will put more load on the screwed joints. As my photo shows a single 5mm screw will hole 60lbs( anvil, clamp, angle plate) so lets say 25kg per screw. You don’t say what size your frame is but lets assume a 600 x 1200 with one cross member in the middle. Put screws at 200mm cts along the five frame members as that is a total of 21screws.

21 x 25kg = 525kg so even if you could lift that much it is unlikely that the screws will pull out before your arms come out of their sockets.

Now you have said you want to put “heavy” equipment onto the bench. As I have said in this situation the load is all downwards so the screws really only stop the worktop sliding off the frame if you wheel it into soemthing and stop suddenly so no really worries about screw loading there.

Main thin for the last issue is to ensure loads go directly down through worktop, to top frame which sits on the uprights which sit on the casters then all loads are taken by the compression of the materials not by any joints. Most likely failure of a structure like this would be twisting due to lack of triangulation rather than any component failing under compression loads.

As for bolting through the whole thing just watch if there is coolant splashing about as you don’t want moisture getting into the chipboard. Also if counterboring and plugging the holes you will then have your bolt head bearing on the less dense mid layer of the chipboard and not the denser outer layers.

Here is something supported by unistrut, soliid glass basins are 50kg each, ceramic top , metal draw runners and several sheets worth of board, glass fronts and overhang when open. 6 small screws hold it to the horizontal unistrut members and me and my glass guy stood on it to fit the mirrors so downwards loading needs minimal screwing. Though I did not use plugs and screws to hold the unistrut cantilever brackets to the wall behind. All to do with thinking about what loads here are and how they act.

 

[Andrew TinsleyParticipant @andrewtinsley63637]

Hello Jason,

I am perfectly aware that if I put heavy kit on the bench. I don’t even need to fix the worktop down. I just wanted to give some idea of the usage.

The framework is very heavy, I have just done an end for end weighing and the total is approximately 180 Kilos (without worktop)! So you can probably work out why I am concerned at lifting it by the end of the worktop.(probably by jacking) I will  need to do this lift for several reasons. I don’t think that the main outline material is Unistrut after all. It is at least 55 years old and there is a large amount of 2 x 2 angle making up frames for draws and cupboards.

Not being a woodworker, I am not confident that simple woodscrews are going to do the job.

The idea of bolting plates came from Howard, not me. Although I am happier with the idea of bolts rather than screws as is natural for anyone of my background.

Regards,

Andrew.

[Andrew Tinsley]

On Andrew Tinsley Said:

Hello Jason,

 

Not being a woodworker, I am not confident that simple woodscrews are going to do the job.

 

I had hoped that my photo showing a screw supporting 27kg would give you some confidence. If you use the amount of screws I suggested you will only be hanging 8.5kg off each one when you lift the 180kg frame. As worktop is being lifted by the jack it’s weight does not need to be included in what the screws are lifting.

[Mark EasingwoodParticipant @markeasingwood33578]

Well, it’s gone somewhat quite at work, so earlier in the day I embarked on a similar experiment to Jason.

I screwed an offcut of 45mm chipboard to a short scaffold plank with a couple of screws, I then screwed a short length of chain to the chipboard, through the centre link using a 5.0 x 60 mm Hafele brand woodscrew and a washer. I used an impact driver, no pilot hole, the screw entering the chipboard about 40mm.

The plank was then placed, with the chipboard underneath, 1 end on the internal office roof and the other end on a timber rack, about 8ft in the air. The two ends of the chain dangling down.

I proceeded to grab hold of the chain ends, and did a few pull ups. The screw shows no sign of pulling out. So a straight pull of a bit under 10 stone!

No pictures available, as no free hand to take one!!

Mark.

[NealebParticipant @nealeb]

I have a related problem with chipboard and screwed fittings. My kitchen cupboards have simple knobs on. The knob on one cupboard, for some reason, is often catching on a trouser pocket and the screws on one hinge mounting have come loose – pulling straight out of the board. It is fixed into standard 16mm or so board. As it happens, there is an additional facing board at that point so I replaced the screws with longer, to go into both boards. These have now come loose – although, curiously,I haven’t actually torn a pocket yet as the screw fixings are weaker!

What would the committee suggest as a fix? Drill for screwed inserts? I had thought of using a hinge cutter to make a recess to take a hardwood plug glued in. Clearly, the original “screw into chipboard” fixings were not adequate in this case!

[JasonBModerator @jasonb]

Assuming they are the common consealed type hinge then your best bet will be a hinge repair plate which can be screwed to the carcase using new screw positions and the hinge then fixes to that with the system screws captive in the hinge or machine screws and nuts if you just have woodscrews holding the hinges to the carcase.

[NealebParticipant @nealeb]

Many thanks, Jason – looks like a trip to Screwfix is called for! Quick tweak to hinge adjusting screws and job’s done. Haven’t come across these before but always happy to hear from a professional.

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