Clamps

From Ed's Mediawiki
Revision as of 12:33, 14 November 2011 by Eburdick (talk | contribs) (T-Slot Nuts and/or bolts, flange nuts and studs)

Clamps are key shop components for robot work. Uses vary widely, including holding stuff down to the bench for sawing or filing, holding pieces together for drilling, and holding parts on the drill press or mill.

C Clamps

There is a wide variety of sizes and quality. Here are some 4 inch clamps from Home Depot. The blue one is made by Irwin, at $8. The clamping force is not specified, and it just says it is made of "steel". The black one next to it is the same size in drop forged steel made by Jorgensen, and is $20. The difference is the material and the clamping capacity. The Jorgensen clamps at 6200 pounds; the Irwin does not specify clamping force . The third one, also made by Jorgensen but cast, not drop forged, clamps at 2400 pounds, has square threads, and goes for $13. For our purposes, drop forged clamps are probably overkill, but I like the cheaper Jorgensen with the square threads. Square threads make a significant difference in how much effort you need to put into tightening the clamp.

Irwin-c-clamp.pngC-clamp3.pngSquare-thead-c-clamp.png

Deep reach C clamps

These let you clamp to benches, drill press tables, the band saw table, etc, with a lot of distance between the back of the clamp and the clamping surfaces. Careful on this, because they need to be very strong to support this distance and still clamp tight. Three different depths shown below. The deeper, the less rigid, so take some measurements on the machines before deciding.

Deep-clamp.png C-clamp1.pngC-clamp2.png

Bar clamps

Bar clamps can open up very wide, but are not generally as strong as a good C clamp. they are, however, a very good clamp to have around because of the ability to clamp over a large distance. Two bar clamps are shown here, one with a deep reach.

Deep-bar-clamp.jpgBar-clamp.jpg

How do you check clamps for rigidity? How far can you turn the screw after the clamping surfaces meet? My 4" cast clamps with coarse square threads are tight after about 10 to 15 degrees. My lighter duty ductile iron 3" medium deep reach clamps with finer triangular threads are almost tight after 720 degrees. Big difference. Which is more rigid? For the deep reach C clamps, you might want to go with higher quality drop forged construction, and stick with less costly cast clamps for normal reach. But don't get me wrong. The smaller/lighter clamps are very useful. They just don't clamp as hard.

Machine tool work holding

For clamping work to a mill or drill press table, you can use c-clamps, but this is time consuming and awkward. A good drill press vise along with clamping accessories is a very worthwhile investment.

Drill press vise

For precision drilling, a drill press vise with step jaws is fundamental. Good ones can be very expensive, but there is a good range between junk and top of the line. The main things I recommend is step jaws and a way to easily clamp to the table with standard clamping kits, described below. The reason for having step jaws is so that you can hold work at the top of the vise with a "floor" that keeps it parallel to the machine's table. If your vise does not have a precision step, then you must rely on a spacer under the work, or hold it at the bottom of the jaws, which can get in the way of the work you are doing. Some illustrations:

Screw style vise with lug style clamping sites and step jaw. Note jaw also has V grooves for holding round objects. About $200 for 3" jaws

Drill-press-vise-screw.png

Pump action slide bar style with step jaw. About $165 for 3" jaws. No V grooves for holding round objects, but this style has an open bottom for drilling through without having to worry about drilling into the vise.

Drill-press-vise-slide-bar.png

Inexpensive light duty cam action slide bar without step jaw. Slots for clamping. About $50 for 3" jaws.

Drill-press-vise-cheap.png

T-Slot Nuts and/or bolts, flange nuts and studs

These come in different sizes, so you have to check the size of the T-slots where you want to use them. They fit into the table slots on the drill press and are great for holding down a drill press vise, or other clamping fixtures. This stuff is pretty inexpensive, and is much more effective than using c-clamps. As part of this type of clamping system, there are also clamping bars that can be used for holding work directly. Many of these have precision steps as shown below.

Table-clamping-components.png Table-clamping-set.png T-bolt.png Table-clamping-bar.png Table-clamping-bar2.png


You can also get a clamping set that has a lot of of these components for just over $100


Hold-down Clamps. These screw down on the table through the slots. More convenient than C-clamps because they use the table for part of the clamp. These are $20 to $100 depending on size and capacity.


X-Y vise. I got one of these cheap at a Big-Lots type place back east. Sometimes very handy for milling on the drill press. These have a lot of play and backlash, and are not precision tools, but for the right price, they can be useful. This one is $60 at Harbor Freight, which also has very cheap drill press vises (don't know how good they are.)

Toolmakers Parallel Clamps

These look like miniature Jorgensen woodworking clamps, but they work differently. You back off the rear screw, tighten with the middle one and then finish with leverage by tightening the rear screw. These come as small as just over and inch and up to about four inches. These are incredibly useful for holding small stuff, clamping two or three parts together for drilling, etc. A pair of top of the line Starrett clamps with 1.25 inch max jaw opening is $45. But you can get lower end ones that work fine for as little as $5 for 1.25" up to $23 for 4.5"

Tool-makers-clamp.pngTool-makers-clamp-set.png

V Blocks

For drilling round items, it is good to have a way of holding them. The typical thing for this is a V block. The kind with a clamp is nice, but you can improvise with just a block. The examples below come in matched pairs for holding round stock at two points on a machine table. Price range $29.50 to $56.60 for capacity up to 1.5" These can get really expensive for larger work, but for larger work there is usually another workaround.

Vblocks1.png Vblocks2.png