The only way to ensure you get the most appropriate tooling for your requirements is to think about what the tool actually has to do for you. With so many options available, it pays to know about different types of cutters so that you can weigh up the pros & cons against your priorities, e.g. am I going to be able to efficiently cool the tools while in use or do I need a cutter that will keep its edge even when allowed to get blue hot, or will the cutter need to handle an interrupted cut?
The main factors you should consider are listed below, click the titles to see more about each point.
Workpiece hardness
Most basic cutters are HSS, a fairly hard material that is suitable for use with mild steel and softer materials.
Many have a higher Cobalt content and are known as HSS-Co or HSS-E, 5% is a common amount and some go up to 8%, enabling them to cut harder materials. While Cobalt makes the tool harder, it also makes it less forgiving of shock which means high-Cobalt cutters are more prone to shattering in less stable situations.
In contrast, a carbide-tipped cutter uses the cutting power of the harder tungsten carbide teeth but can combine them with a much more forgiving, softer steel body so they tend not to shatter as easily. However, the carbide requires very stable, uninterrupted cutting conditions to avoid chipping and breaking the teeth themselves.
It is worth noting that both HSS and TCT cutters can be resharpened if they are only dulled or slightly damaged, but heavy damage to either is likely to make repairing them uneconomical. Remember that whatever the type, cutters are consumable items and will only take so much use and resharpens before they need replacing anyway.
Your machine’s capabilities will also be a factor here, as harder materials need slower speeds.
Heat tolerance
Standard HSS cutters will, being the softest cutting edges of the types available, generally go blunt more quickly than the others. If they are allowed to get hot enough to change colour, they will also lose their hardness and become unusable.
HSS-Co / HSS-E cutters are gaining in popularity as the additional Cobalt adds only about 10% to the cost but offers much improved heat resistance. HSS-Co / HSS-E cutters can withstand running to blue hot without compromising their cutting ability. They may be more expensive but can cut hotter in harder materials, the only drawback being their higher demands for stability.
TCT cutters are also becoming a more popular choice and in some overseas markets they are already the primary cutter choice. It is important to realise that, while the carbide tips will withstand considerably more heat than an HSS cutter could handle, the solder that bonds the tips to the cutter body will melt if sufficiently heated, causing the tips to literally fly off the tool.
Rough / interrupted cutting
Stability is a key factor in getting the best from annular cutters, but if you simply cannot guarantee the tool is not going to be subjected to rough or interrupted cutting, vibration or other shock during use, TCT cutters are not a good option.
Price & economy
Up to about 40mm diameter, the purchase price of HSS cutters is usually less than that of their carbide-tipped cousins but this is reversed above that diameter.
When measured in terms of cost per hole, it gets a bit more blurry as TCT cutters can drill what an HSS one can’t, and will certainly stay sharp for much longer (and therefore spread their purchase price over more drilled holes) if used in materials such as stainless steel. Coated HSS cutters can improve performance although this is often only significant when drilling in the kind of material that the coating is made for and negligible in less demanding materials.
Obviously, you are likely to get many more holes out of a cutter that suits the material and circumstances that you are using it for, so when comparing types you should also consider factors such as lubricants used, times taken and tool-change downtime, etc. to get a clearer picture of the true costs.
But you may also find yourself in a position where you urgently need to drill a couple of holes in a material or situation that won’t be good for the cutters you have available. In these circumstances, you’ll need to make the best compromise and knowing what definitely won’t be any good will at least help you make the worst choice. For example, if you can only use a TCT cutter can you improve the stability to increase your chances of success, or can you reduce the speed by 60 to 70% if you’re drilling high tensile steel with a marginal cutter choice?
Summary
Annular cutters are consumables and often they must be used in conditions that are not ideal, so to get the best value you need to make an assessment of your priorities for the job at hand.
Where you can, choose a cutter that has the abilities to match the job’s demands as much as possible. When this is not realistic you should understand the pros and cons of the different types and make an informed judgement of where to compromise.
Ensuring that your mag drill operators have a sound understanding of the factors that affect cutter performance will also help them monitor the tools during use and improve the overall results.
If you want to know more about how to increase the life of your annular cutters, see our article HERE, or for help on getting better hole quality from them, read THIS ARTICLE instead.
Looking for advice on how to choose your new Mag Drill? THIS ARTICLE will help.
