Plastic or other Hold Down Clamps

So the kitchen remodel is finally coming to a close. Seems like forever but now I have time to play with my new CNC router, again.

I have been using the hold down clips that came with it, but they are steel and its a real challenge keeping them out of the router path. I have some of the double faced tape ordered but I think plastic hold downs are a better solution.

I have a 3D printer so that might be one way, but not sure of the strength.

Any suggestions? My plan is to develop a add on segment to my laser engraving business, big enough I need to purchase a Cam Master or more pro machine!

I've become a real fan of the Legacy LowPro clamps. They're pricey, but very convenient since they clamp from the edge. Unlike so many other side pressure systems, they force the edge down to the table rather than lifting it.

For things with close tolerance, it seems practical to just make wood/plywood low-profile clamps that are similar to the ones that you likely have already but are metal. Some I've seen in videos are made from material like 1/2" plywood with a rabbit in the end that keeps the portion over the workpiece to something like 3/16"-14" thick max. That provides a lot of tool clearance in case you make a boo-boo and with no metal near the workpiece, it's less likely to kill a cutter.

There are so many ways to hold down work it seems! One way that's becoming pretty popular it seems is the masking tape and CA glue thing as a substitute for expensive double-stick tape. It's probably not good for really large workpieces, but for smaller things, it eliminates the clamps altogether. Tape/CA combined with indexed alignment pins or similar can help with repetitive tasks, too.

And yea...I hope you can build things up so you can add a bit of school bus yellow to your shop! :D

The LoPro clamps are way pricey, looks like they intend to pay for the new CNC machine in just a few orders! I ordered some of the side clamps from Rockler just now along with the angled mini aluminum ones. I could make some out of aluminum I have in the shop to supplement.

I made some eccentric clamps out of wood for the odd project. They work ok, but do tend to lift the stock along the edge sometimes. You can buy the mittee bites from McMaster Carr too. Those do not give you much movement allowance, but they are very low profile and hold very well since the force is applied perpendicular to the stock.

Here is a pic of my simple wooden eccentric clamps. I do not use them much anymore since adding vacuum solutions. I expect you will go to a vacuum setup fairly quickly. You need your stock to sit down perfectly for engraving or other operations involving fine cuts.
Attachment 380725

Here's an interesting video by James McGrew around work holding with some good observations about how certain clamps work or not. It doesn't cover everything, but it can be useful.

https://www.youtube.com/watch?v=JEJ6rRgFfT4&t=86s

I never use plywood or hardwood for that matter. I make my hold downs from 3/4" PVC sheet, cut them on my band saw so I have a small lip that sits on top of the material. PVC won't separate like plywood and even if the router bit hits the PVC it cuts like butter. Most of my work is held to the table with screws but you can easily adjust the PVC style hold downs to fit your table style.

Attachment 380742Attachment 380743 I make these in a variety of lengths and drill several holes so I can increase the holding pressure by moving the screw closer to to the material. You can see that the PVC piece on the lower right has been hit by a router bit.

Attachment 380744Attachment 380745 This is an auxiliary clamping table that I install when I need a special fixture or when I have an odd shaped piece. In some instances I use the step blocks commonly used with milling machines but the PVC pieces work on this table as well.

Attachment 380746 I have a couple of drawers that I keep a variety of clamping items handy including four of the Grizzly edge clamps that Jim McGrew mentioned in his video.

This is just my day to day method of holding material to my table, there will always be projects that require a unique hold down method particularly when mass producing custom parts.

Here is a thread that shows my setup for holding tall wooden pieces for some candle holders I made for Christmas presents using aluminum angle. https://sawmillcreek.org/showthread....ghlight=candle

I hope this helps.
.

That's a good idea about using the PVC, Keith. Thanks for mentioning that!

Quote:

---

Originally Posted by Keith Outten

I never use plywood or hardwood for that matter. I make my hold downs from 3/4" PVC sheet, cut them on my band saw so I have a small lip that sits on top of the material. PVC won't separate like plywood and even if the router bit hits the PVC it cuts like butter. Most of my work is held to the table with screws but you can easily adjust the PVC style hold downs to fit your table style.

Attachment 380742Attachment 380743.

---

I like those clamps. I have been making a similar type clamp from wood scraps, but like you mention, many of them eventually crack. The tips are also slowly getting carved away. I consider them to be consumable.

All good ideas, and the plastic is disposable. Thanks for posting.

The PVC blocks can be cut to any shape when you need to hold down an odd piece. It flexes easily and will hold very tight as well using multiple holes to adjust the tension. I keep a couple dozen of these on my CNC Lathe rails and have a few that I haven't cut the notches in case I need to hold down material that is an odd thickness. The normal notches i cut fit everything from 1/2" to 3/4" thick material.

I plan to use PVC for my next spoil board rather than MDF.

I'm curious - why PVC rather than HDPE, UHMW or ABS? Is the PVC stiffer?

Quote:

---

Originally Posted by richard newman

I'm curious - why PVC rather than HDPE, UHMW or ABS? Is the PVC stiffer?

---

Ready available and cheap easy to cut

I had never thought of using PVC sheet material. I have scraps laying around all over the place from old sign projects. I have always just used wood. I make a lot of the same thing so it pays to build dedicated fixtures that set up quickly. A lot of clamp designs, like what McGrew was showing, use a cam action but I have found pairs of opposing wedges are easy to make yourself and they work better for what I do.