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Tips for Drilling and Tapping
​Drilling and tapping is one of those skills that are often taken for granted by farriers. It seems so simple a skill that most farriers don't think much about it at all. In reality, the motions are simple but its a very technically complex process. A little bit of time spent on fine tuning your process can safe you time and money.

Setting up a drill press

Taking care in setting up your press will make the whole job easier. When setting up a drill press we are concerned about 2 things: run out and rigidity.

Run out is when the drill bit does not spin perfectly on the axis. Usually its the result of the drill bit being slightly crooked relative to the spindle so the longer the drill bit or the farther out in the chuck its held, the worse the run out becomes. Every drill press has some degree of run out. High quality drill presses generally have less run out on average than cheap drill presses. Excess run out shortens the life of your drill bits and causes oversize or out of round holes


Rigidity in this application is the strength of the drill press to hold the drill bit and the shoe in the same position relative to each other. A good illustration of lack of rigidity is when a drill bit “walks”. Poor rigidity makes run out worse, makes the setup prone to chatter, and makes it difficult to drill a hole where you want to drill a hole.


To get the best performance from your setup:
  • The drill chuck should be cleaned before changing bits to make sure there's no metal chips in the mechanism or on the jaws. This minimizes runout
  • The drill bit should be placed as far into the chuck as possible while still clearing tops of the flutes. This minimizes runout and maximizes rigidity.
  • The table should be set as high as possible while still clearing the shoe so the spindle doesn't have to be extended any farther than necessary. This maximizes rigidity
  • The drill press table should be squared to the spindle. This minimizes runout by keeping the drilling forces square.



To square the table to the spindle you can put a piece of coat hanger in the chuck, cut it and bend it so that the end is sitting just above the edge on the side of the table. Then spin the chuck so it sweeps across the table. Adjust the table so the space between the coat hanger and the table is even on each side. You can lower the spindle as you get the adjustment fine tune until you have the coat hanger lightly grazing the table in the full arc when the table is perfectly level.


​Its generally accepted in industrial metal working and machine shops that any metal being drilled must be held firmly in a vise for safety reasons. Its the best way to keep a workpiece flat, level, and rigid. As farriers we don't do this because no 2 stud holes are in exactly the same place so the setup is time consuming. Its a risk though that increases the likelihood of chatter or catching a bit in a hole and spinning a shoe, breaking a bit, and potentially causing serious injury.


Drill bits catch for 2 reasons: 1. When the shoe is allowed to rotate slightly along with the drill bit like when held in place by hand, the bit takes a deeper bite in the metal, pulling the shoe harder, causing it to rotate more and take an even deeper bite, unless its stopped it'll break the bit or rip the shoe out of your hand. 2. The shoe is tilted with the bit in the hole so the sides of the flutes bite into the metal along with the tip.


This part is a challenging issue to overcome which is why we developed our drill jig. It provides a level surface for the shoe that clears the clips and a post against which the shoe can be braced to keep the shoe from rotating preventing it from catching and if for some reason it were to catch, to keep it from spinning.  

Feeds and Speeds
In machining, feeds and speeds are some of the most critical variables in getting a job done. “Feeds” in this case, refers to how fast the drill bit moves down through the metal. Its typically referred to in inches per minute or inches per rotation mean (how big of a bite the bit takes per rotation). “Speeds” refers to how fast the drill bit is rotating. Its typically referred to in RPM or in surface feet per minute which is how fast the two metals on the outside of the bit are moving relative to each other.

Surface feet per minute and inches per rotation are useful for understanding the limitations of a cutting tool but for a farrier with a drill press in their rig, it doesn't matter. Running a decent O diameter drill bit to its limits requires a drill press with a motor much larger than what anyone carries in their rig. Even with a 1 ½ hp spindle its difficult. Most drill presses in shoeing rigs are 1/4-1/2 hp with the biggest ones being 2/3 hp.

The limiting factor in drilling performance with any good quality O diameter or 5/16” drill bit is torque. There's no point in running a high RPM because what gets the job done as fast as possible is feed rate, not RPM, and feed rate requires torque. As such, most drill presses should be set on the pulley with the lowest RPM, which maximizes torque.

With the maximum torque available, the best feed rate possible can be achieved. Feed rate on a drill press is a lot harder to gauge than a mill. It has to be done by feel and by looking at the chips that are produced. Its important to have a high enough feed rate that the cutting edge takes a good bite of material consistently. When the cutting edge is fully engaged and stripping off a continuous strip of material, the heat from the cut goes into the material being removed and taken away. When the cutting edge is barely engaged, it bounces in and out of the cut and rubs on the surface of the material, creating chatter and a lot of heat that stays in the cut. This heat can build up and ruin your drill bit.

When drilling you should be watching the chips that are being produced and ensuring that they are large thick chips instead of fine rough, inconsistent chips that indicate that the feedrate is too low. Its easy to judge when the feedrate is too high because the motor will stall.

A demonstration of the effect of feed rate. On the left you can see an appropriate feed rate and on the right you can see a feed rate that's too slow notice the difference in the chips that are produced. 
Lubrication

HSS and Cobalt bits require cutting oil. Cutting oil reduces the friction of the cut and reduces heat. Oil must be regularly added during the drilling to be effective as its quickly removed from the hole. Wax or stick lubricants are less messy and end up saving money since its easier to get the right amount of lubrication in the right place. High quality coated carbide bits like our countersink bit don't require cutting oil due to the coating and high heat resistance of carbide.

Chamfer

It's critical to chamfer every hole that will be tapped to protect the threads and help with starting the tap in the hole. Chamfers (or countersinks) are available in a variety of angles but the correct ones for this purpose is the 82 deg or 90 deg kind. The total diameter of the chamfer once cut should be slightly larger 3/8” but not too much larger as a deeper cut results in less threads.
Tapping

There are a variety of methods to tap horseshoes. The most basic is a simple tap handle. Then there are tap guide set ups like the Valley Tapper that is basically a large tap handle with a guide. The fastest method is using an impact driver. Impact drivers accept 1/4” hex drive bits and have an impact action like the air impact guns used by mechanics to create a force higher than otherwise possible.

To tap with an impact gun you need a 1/4” hex drive to 3/8” square drive adapter, a tap holder, and a tap. Lubrication is absolutely necessary with all taps. It reduces the force required turn the tap which is critical to tap life. We recommend using a wax type lubricant as its less messy and allows you to load lubricant where its needed.

The most important factor to successful tapping and preventing broken taps is alignment in the hole. By using plug, spiral point taps in a tap chuck, the tap can self align as long as you are close due to the taper shape of the tap and the play in the tap chuck joint that allows it to center itself.

As the tap starts to cut, its important to watch and make sure its aligned in the hole correctly and if you are using spiral point taps, its not necessary to stop and back out the tap unless it suddenly becomes difficult to turn. Taps can suddenly become difficult to turn due to trapping a metal shaving or by chipping or dulling a cutting edge.

Check the edges of your taps often and if they become chipped or dull or the tap is consistently hard to turn, replace it before it breaks as a new tap is cheaper than the time spent trying to remove a broken tap or making a replacement shoe.  

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