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Thread: Woodwork Bench design issue.
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5th March 2017, 09:39 PM #1New Member
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Woodwork Bench design issue.
I have finally started making a workbench out of timber that I have salvage form construction sites, I have made a skirt out out 180 * 45 (8"x2") treated pine. The legs are 90x90 (4x4) pink primed pine posts that have had 20mm checked out and then been bolted onto the skirt. Two carpenters vices go through the skirt on the front left and right. There are four support members that run from the front skirt to the back skirt to support the worktop and for dog holes. I am gluing together 2 pieces of 12mm (1/2") pine plywood for the top to make the top 24mm thick). Although this is a carpenters workbench I am more like a general handyman than a full on fine carpentry type carpenter. For this reason I have gone with plywood as it is easy rather than make the entire worktop by laminating studs together.
I am having trouble with the support members that run from the front of the skirt to the back. I will be drilling dog holes in them as I hope to use hold downs (these ones have a screw adjustment like an F Clamp), timber dogs and wonder dogs. Given that these members will have 20mm (3/4") holes bored through them I chose to use some really old red hardwood. The members are 90mm (4") deep x 50 or 65 (2" or 3") wide. I want to make sure that if I put a fair bit of force on a hold down that is facing the side, that it will not split the support member.
I tried using 6mm (1/4") x 130 (5,1/2") (Zenith Brand) galvanized coach screws (lag screws) through the front and back skirts and into the end grain of the support member. But the screws keep snapping in two, between the skirt and the support member. So I tried bigger pilot holes and the screws either pulled out or they snapped again. I went back to the hardware shop and got 8mm (5/16") x 130 (5,1/2") coach screws and the same thing happened. I even used my clearance drill bit and drilled half of the depth in the hardwood to limit the stress on the coach screw and the coach screws still snapped.
At this point I am assuming that this hardwood is not ideal to be using coach screws on (that and the coach screws are using too soft a steel). Some ideas I had to fix the issue are. Use some of the 90mm x 90mm laminated pink primed pine posts I have left lying around instead of the hardwood. I could put the laminations horizontally to help stop any splitting. That way I could still use coach screws to hold the support member in place. Perhaps even put a 50mm (2") 8g screw either side of the dog hole to brace the support member.
Could anyone suggest how they would solve the problem or give details of how they built a similar workbench. Any ideas will be greatly appreciated. Thanks )
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5th March 2017 09:39 PM # ADSGoogle Adsense Advertisement
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6th March 2017, 02:26 AM #2
Hi raven
welcome to the forums.
1. what is most likely happening is that the coach screws can't drill their way into the hardwood end grain and are jamming and then breaking when you torque them up. Ideally the pilot hole should be around the same diameter as the base of the screw thread and the same depth as the screw is long. If the screws still break, enlarge the pilot hole to a diameter that approaches the outside diameter of the thread.
2. in terms of your design, I suggest that the cross members be arranged so that the 90 mm dimension is parallel to the bench top. 50 or 60 mm of depth will be plenty deep enough to span the width of a bench and with the 24 mm thick top (total depth 70 to 80 mm) have more than enough meat for hold fasts and bench dogs.
3. coach screws into end grain don't have the holding power of screws into side grain. But being hardwood and a bench, they may work for you long term. If over time they become a little loose you can fix the problem by installing 12 or 16 mm diameter cross dowels.
4. design issues.
a. A single front vice -- at the left of the bench if you're right handed -- is almost certainly a better choice than two face vices.
b. Install the second vice as an end vice at the opposite end of the bench to the face vice.
c. glue battens to your front apron between the cross supports, into which you can drill dog holes for use with the end vice.regards from Alberta, Canada
ian
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6th March 2017, 08:54 AM #3Senior Member
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have you considered applying some form of lube ,grease is pretty good on the coach screws?[not too much if you intend to apply some form of finish to bench or the grease will stain]
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6th March 2017, 09:23 AM #4
You probably need to use something like these bench bolts rather than screwing into endgrain. You can bury a normal nut and washer in the cross piece, it doesn't need to be a brass dowel.
Franklin
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6th March 2017, 10:27 AM #5.
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I'm a big fan of this style of connection and have even used small versions when joining aluminium tubing.
It produces a very strong connection that can be easily tightened if required.
If you cut the bolt hole with a hole saw you can cut a semicircular slice off the material that comes out of the hole and use that as the circular washer.
Make sure you arrange the grain in the wooden washer to run perpendicular to the hole - if the grain is parallel, tightening the bolt will snap the washer.
If you want a more neatly fitting washer you will have to cut one from another piece of wood.
Screen Shot 2017-03-06 at 7.18.11 AM.png
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6th March 2017, 01:07 PM #6GOLD MEMBER
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Welcome to the forum Raven.
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6th March 2017, 10:20 PM #7
Welcome, Raven
Those coach screws that you mention are absolute crap, renowned for having detachable heads. Even though they may be labelled 6mm, check their sizing - bet its different!
Suggest that you go to a specialist fastenners store and buy some real coach screws or, better still, some bench bolts as suggested by Franklin and Bobl.
Cheers
Graeme
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7th March 2017, 01:34 PM #8
You can use normal bolts to save a few bucks. I did this to attach my bench legs to the long side rails. Normal washers too. Just square off the hole with a chisel.
Regards
John
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22nd March 2017, 01:01 PM #9Senior Member
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cheap bench bolts
Cheap bench bolts - great service.
https://mcjing.com.au/searchresult.a...d=bench%20bolt
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23rd March 2017, 10:11 AM #10
Certainly better, but still quite a lot more than you need to spend, NE. - 200 x 10mm bolts were a few $s apiece, last time I bought them. Barrel-nuts appeal for the looks, but I can tell you from experience that they are a right pita to fit. It's exceedingly difficult to drill the intersecting holes with the accuracy required, & if you get them off, a lot of fiddling & enlarging of the holes may be required to get them to take up! I rout a slot with a 1/2" bit instead of drilling the space for the nut, gives lots of room to get an open-end spanner in there, but Orraloon's method has great merit, because if you make the cut-out a neat fit, it captures the nut and you shouldn't need a spanner when undoing or tightening the nut. Of course, I could chop out a nut recess in my routered slot, now you've pointed out the bleeding obvious, John!
Agree with Bob, this method makes a very strong & sound joint. The stretchers on my bench have given no trouble at all in the close-to 30 years since I built it. I check them occasionally, but have not had any come loose, yet...
Cheers,IW
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23rd March 2017, 11:33 AM #11
I've done pretty much as John describes, it allows use of a washer and room for the bolt to be drawn into. A spanner can also get at the nut if needed.
However, has the original poster ever been back here?Franklin
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23rd March 2017, 12:33 PM #12
Can't tell, Franklin, unless he replies, the counter only records you once.... But 103 others have read the thread, so far, and there's been a good discussion, and I picked up a tip from John (so obvious, but I hadn't thought of it myself!), so all's well in our little world, I think.....
Cheers,IW
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23rd March 2017, 03:53 PM #13
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