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The Glanze Boring Bar on a mini-lathe

Solve all mini-lathe boring problems with Glanze Boring Bar

The Glanze boring bar has transformed the operation of boring a hole on the mini-lathe from a chore to a delight that I look forward to.

When turning metal it is often required that a bore is enlarged to a specific size. You can perform this sort of operation using a Reamer or by Boring.

A Reamer is a fluted cutting tool that will enlarge a hole to a very specific size. Well. Not quite true. If you need a hole in something to be 0.250", what you actually need is either 0.251 or 0.249. The smaller hole will allow you to press fit a shaft into the hole. You might need to warm the part with the hole and and chill the shaft, but once the two are mated together, nothing will bring them apart, except a big hammer or large press.

The large sized reamer will make a hole in which a 0.250 shaft will rotate freely. This sounds good, but if you needed to by a reamer for every different sized hole you need to make, you will soon run out of money. A decent reamer to bore out to 62mm might cost more than my lathe!!

The other approach is to use the technique of boring. This uses a lathe tool to slowly enlarge the hole to the required sizes. The tool used is normally referred to as a "boring bar".

For a while I was using the boring bar that was supplied with the mini-lathe - a simple carbide tool. It did the job ok, but wasn't anything great. Well, I didn't realise how bad it was...

I have two main problems with boring. The first one is measuring how big the bore is. It is difficult to measure the inside of the bore, even with calipers, micrometers and telescoping bore gauges, however, the problems produced by cheap boring tools are far worse.

Cheap boring tools bend. The more metal you are trying to remove, the more the bend. So, if you are trying to do, say, a 0.010 cut, you'll only remove 0.007, for example. This means that it is very difficult to get a constant inner diameter down the length of the bore. It is also likely that the tool will "bounce" over irregularities in the surface - making a really tight fitting bore with an inner diameter accurate to 0.001 very difficult to achieve.

Enter the new boring bar. I purchased a Glanze boring bar with one of those little insert tips. This tool was not cheap, about £15, but it is a magic tool! My boring experience was transformed by using this tool. I would remove 3 times as much metal with each cut using this tool instead of the carbide boring bar, and it gave a much smoother finish. In fact, it gives such a nice finish that I often use it for facing and other operations.

I cannot recommend this type of tool highly enough. You can buy them from most machine tool suppliers in the uk. I got mine from Chronos. It is ideally suited to a mini-lathe. The shaft of the tool has flats on it that easily fit into my Quick Change Tool Post. The thickness across the flats is 9mm.

I've done quite a bit of boring with the bar in these images, but it still cuts well and I haven't needed to change the insert for a new one using the supplied tool. There are 2 spare inserts with the tool.