Hold Down Design

discussion of design changes / improvements / suggestions
Post Reply
RaymondOverman
Posts: 50
Joined: Tue May 20, 2014 8:13 pm

Hold Down Design

Post by RaymondOverman » Fri Jun 06, 2014 11:14 pm

I took a page from the guy who made the hold downs with Harbor Freight wood clamps and put together this idea.
WP_20140606_17_44_46_Pro (Medium).jpg
WP_20140606_17_44_46_Pro (Medium).jpg (283.75 KiB) Viewed 4681 times
A friend of mine that works in a cabinet shop gave me three pieces of, what I think is, inch thick Delrin. I made two blocks to guide some 3/8" all thread and threaded a piece that will work as a stretcher across the bed. I have various widths of scrap maple that will act as filler to keep me from having to turn the all thread so much. I'll eventually put a belt between two pulleys I made for each side and I can use a cordless drill to tighten or loosen the grip.

Pros:

1) No holes in the wasteboard
2) No hold downs in the way of bits
3) Full width and length of X,Y travel available for milling

Cons

1) Limits length of material
2) Possible pulling up on material
3) Limit to length of material that can go in the bed

I'm sure there will be more things I discover when I have a chance to use it for a while. I'll have to incorporate any changes into V 2.0
SO2 / NEMA 23s / 5 axis SainSmart BOB and Drivers / DW660 Spindle / Rotary Axis / Spindle-Vac Relay / LimSW / Fender Wells / Drilled and Tapped 1"x8TPI Waste Board

deejayspinz
Posts: 96
Joined: Wed Oct 17, 2012 9:33 am
Location: Burlington Ontario, Canada

Re: Hold Down Design

Post by deejayspinz » Sun Jun 08, 2014 11:15 am

I've just found my next project.. Thx for sharing!

Woodworker
Posts: 639
Joined: Tue Mar 11, 2014 1:37 am
Location: 5 miles north of Benson, NC

Re: Hold Down Design

Post by Woodworker » Sun Jun 08, 2014 12:24 pm

To help stop the tendency to pull up, you can bevel the edge that comes in contact with the part. Doesn't have to be a lot. If you have a table saw, just set the blade at 2 to 3 degrees and run the block through. If the maple is dedicated to the clamp you could dowel the pieces without glue so they would interlock. This is a great idea, thanks for sharing it.
BRuce - SO2 #4798 - IC's Z axis upgrade, customized Z rail and Z motor mount, spindle Dewalt 611

RaymondOverman
Posts: 50
Joined: Tue May 20, 2014 8:13 pm

Re: Hold Down Design

Post by RaymondOverman » Mon Jun 09, 2014 1:16 pm

With what testing I've done, I haven't had any problems with it pulling up. I haven't had a need to do any deep cuts however and I'm probably going to move to a DW660 next week. I'll see how it works with the new spindle and update this thread with any further information. Considering I can pick the machine up with a piece that's clamped I doubt I'll have any problems.
SO2 / NEMA 23s / 5 axis SainSmart BOB and Drivers / DW660 Spindle / Rotary Axis / Spindle-Vac Relay / LimSW / Fender Wells / Drilled and Tapped 1"x8TPI Waste Board

cvoinescu
Posts: 4442
Joined: Thu Jul 19, 2012 6:50 pm
Location: Camberley, UK
Contact:

Re: Hold Down Design

Post by cvoinescu » Mon Jun 09, 2014 1:30 pm

The only problem I see with sideways clamping is cutting profiles in the direction parallel to the jaws of the clamp. The clamp can squeeze the cut, which can cause the part to move or the bit to break, although the remaining stock should withstand most of that force. Maybe when you cut profiles, add shims so that the force is applied only on the parts of the stock that will remain intact (the ends). If you don't cut all the way through the material, though, this system is very handy.
Proud owner of ShapeOko #709, eShapeOko #0, and of store.amberspyglass.co.uk

RaymondOverman
Posts: 50
Joined: Tue May 20, 2014 8:13 pm

Re: Hold Down Design

Post by RaymondOverman » Mon Jun 09, 2014 2:40 pm

If that became a problem I could always run a short screw through the stretchers into the material. There isn't a lot of pressure required to hold the material since there's a lot of surface area contact creating friction along the sides. Also, the pressure on the delrin stretcher side is concentrated at the corners so I don't see a profile cut creating a pinch point unless I'm cutting all the way across the X axis. Time will tell.
SO2 / NEMA 23s / 5 axis SainSmart BOB and Drivers / DW660 Spindle / Rotary Axis / Spindle-Vac Relay / LimSW / Fender Wells / Drilled and Tapped 1"x8TPI Waste Board

rtroiani
Posts: 5
Joined: Thu Jan 12, 2017 12:12 am

Re: Hold Down Design

Post by rtroiani » Fri Jan 20, 2017 12:54 pm

Great idea. I think adding some glue-on sandpaper to the faces contacting the would should be sufficient to hold side slippage.

Post Reply