Weekend Bench #9: Some comments on the twin screw

In my last installment I ran through my basic install criteria for the twin screw and how I chose to build the bench mount and vise chock. I left off waiting for some brad point drill bits and some longer bolts to mount the vise with.

Brad point bits arrived yesterday.

They are huge! Near 8in of fluted cutting capacity. Can’t wait to try these things out. First I have to clean off the cosmoline or whatever they shipped them covered in.

I had already jumped the gun and mounted the vise the day before. I got some good ideas from Kem’s blog ( http://lumberjocks.com/jocks/kem/blog/5211 ) and from the LeeValley twin screw instructions on their site ( http://www.leevalley.com/wood/page.aspx?c=2&p=45114&cat=1,41659 ). I had not considered using wear blocks, but I think I will install some shortly to minimize sag. I also really like the steel pins used to keep the wood from contacting the twin screws. That will avoid damaging edges and remove the posibility of thread lube transfering to the piece.

I gotta say, this vise is a beast.

No problem what so ever holding this 9ft board with 6ft+ unsupported. I did discover one flaw to my bench though. With this long of a lever arm you can actually flex the benchtop! Not expecting that one. It actually uses the screw locations to flex the benchtop over the leg. Pretty wild. I may hve to take a video of it before I reinforce against it. Not that I would ever work this way but I still think I am going to pull the bench top and add stringers from leg to leg to prevent this sort of flexure.

Another design issue.

Not sure it really photographs well but here it is none the less. The screws actually pull the mounting block. Serious leverage on those puppies. I used 4 1/2in x 7in bolts to mount the vise block to the bench. When cranked down the screws pull the block untill all slack in the bolt hole is used up. I am going to try using 3M supper 77 to tack the block. If that doesn’t work, then I will be forced to actually use a permanent glue. I can’t have this block moving around on me.

The last issue I encountered was on the chock itself.

The vise screw collars that the chock is mounted to have a fair amount of play. How much? I dunno, I didn’t get out the calipers. I knew that this one was coming, but figured I would put it up here for the crew. Basic fix is to taper the chock so that when clamped it is flush at the top and the bottom gap closes as additional pressure is applied. The Veritas instructions mention this as well and give an number that agrees with how much play their vise has.

Okay, on a brighter note Zoe is getting to be a big girl.

Before long she won’t be leaving puddles in the shop :)

Time log: 33hr

-- Doug, woodworking in Alabama