Mill/Drill Tips

  1. Tip number one is don't buy a mill/drill! Save your pennies, scour the used market, but try like heck to buy a mill with a knee. There are some inexpensive imports, or you can look for a used Bridgeport. There are also some other quality mills that are lesser known like Tree, Clausing and Hardinge (usually known for lathes). If you can get a mill with a knee, most of the other mill/drill tips here will prove unnecessary. If you have to get a mill/drill, try to get the heavier model. It's often known as a #30, like my Grizzly G1006. It's probably best to avoid the power feed options unless you really need them- less to go wrong.
  2. Disassemble the table section of your mill/drill and break all the sharp edges. Be sure all sand and debris is removed, and that lubrication holes are free. Stone the table surface to remove the inevitable dings and dents. Get some real way lube from a tool supply company and lube everything liberally during reassemble. Don't try to get by with a regular oil.
  3. Acquire the minimum necessary accessories to do good quality work. Many problems that the beginner blames on the tool are the result of improper setup and tooling. I'd suggest a good mill vise, full set of collets, a mounted Jacobs chuck, an adjustable work stop, a center finder, and some parallels, as a minimum. Naturally you'll need an assortment of end mills, center drills, and drill bits. Some clamps and supports will also prove handy. Sooner or later you'll also want a boring head. Buy a 2" model as the larger ones will shake the head too much. Take whatever junk vise came free with the mill and put in on the drill press or in the trash where it belongs.
  4. The biggest problem using the mill/drill is setting depth of cut. The feed dial is reasonably accurate, but the travel is limited. There often isn't a good surface to reference to. This is where an almost forgotten technique becomes valuable again. Back in the days of surface planers machinists used a planer gage to set the cutting depth. This is nothing more than a steel ramp with an adjustable piece that moves up and down, usually 2" or so. They are still available, but tend to be expensive new. They can often be obtained used for a few tens of dollars. Try to get the extension plugs that normally come with it. The gage is set on the surface plate and the movable piece is set to the desired height with a vernier height gage. You can also just use a micrometer or verniers. The gage is then placed in the mill/drill and the (non-running) end mill is brought down to just touch. This sets the cutter height above the vise. Lock the cutter. The part is now put in the vise and cut to height. With care the result will be within plus or minus one to two thousandths of an inch.
  5. Being less rigid than a "real" mill, vibration is always a problem. In general, slower speeds and slower feeds are the rule. Light cuts help, though if everything is right substantial metal can be removed quickly. Follow the advice of the end mill manufacturer and the tables in Machinery's Handbook. An important part of this is very sharp tooling. If you're using free used end mills from some friendly machinist, try some new ones. Experiment with coolant. I use an imported water soluble oil for most things, and the higher tech "Cool Tool II" for steels and tougher materials. A spray mist lubricator works well, but avoid breathing the stuff. I keep a big spray can of WD-40 around for aluminum. When a light cutting operation is running correctly, there should be some sound of cutting, but mostly the motor running. If the mill/drill frame is vibrating like crazy, or you hear a knocking sound, back off and troubleshoot the problem! You may be taking too much off, the tool may be dull or the speed and feed not correct for the material. Heavy cuts will be noisy but it shouldn't sound like you're abusing the machine. The sheet metal belt cover tends to make more noise than anything else.
  6. The vibration issue is the biggest strike against the mill/drill. It appears to be the result of the base flexing, not the post. It might be possible to reinforce the base or mount it to a more substantial plate, but the key would be to tie or support the central area between the table and the post, such that the post can't flex fore and aft. Just bolting the base to another plate is unlikely to improve things as much as is needed. Some people have tried filling the post with cement, but that's not the root cause of the problem. If anyone figures out a good way to improve the base, please publish it on the web!
  7. Watch your RPMs. Nothing takes the corners off expensive end mills faster than exceeding the recommended SFPM (surface feet per minute) for the material. For instance, plain steel should be cut at about 100 SFPM with a HSS end mill. That's only about 800 RPM using a 1/2" end mill. If you start out too fast, thinking you'll slow down if necessary, it's too late. You will have toasted your end mill the second you start cutting. Start slow and work up.
  8. I haven't tried this on the mill/drill, but changing the belts to Fenner link belts has done wonders to reduce vibration on my other equipment. Just be sure to buy the right width belts, as the mill/drills often use a wider series of belt. The Fenner belts are quite expensive so I recently replaced my OEM belts with BX series Goodyear Torque-Flex belts. The BX series has notches in the ID so they're better suited to going around the small motor pulley. They're also simply much higher quality belts, much more uniform than the OEM belts. Sure enough, the change helped the vibration issue quite a bit. Surface finishes are about twice as good. My #30 mill/drill uses a BX32 (35" outside circumference) on the motor side and BX40 (43" outside circumference)on the spindle side. My OEM belts were mismarked for size by a couple inches, so be careful about just using the numbers on the belt.
  9. The mill/drill spindles are actually quite well made, using tapered roller bearings, but aren't sealed all that well. If you use an air blast to clear chips from parts in the vise, you can blow chips up into the lower bearing. There are also (typically) two slots in the quill. If you get chips flying with the air blast, and the quill is lowered, they can go right in the slots and land on the lower bearing. The purpose of those slots is a mystery and if you disassemble the spindle, it might be a good idea to insert a thin plastic or metal shield to seal them off. An additional flat slinger just above the lower cap would also be a good idea.
  10. Get the mill/drill at the right working height. Build a sturdy support so you can see what you're doing and don't have to bend over too far for every setup.
  11. Wear your safety glasses! Just one errant chip can result in disaster.