Setting Cutter Height
Hi all.
Bogs is back with a series of Top Tips to build your workshop machining skills.
As some of you may know I have had some serious family health issues to face over the last few months. I am glad to report that for the moment things are looking a little better but it has meant that I have been unable to contribute in the way that I had hoped to John’s website.
John has tried to keep my section of this site up and running for me and has added a few odds and ends into the Bog’s area, to try and keep things interesting for our regular visitors.
Circumstances continue to prevent me from writing long descriptions at this time, so in agreement with John, I will be digging into my fund of archive material, accumulated from my postings on various sites over the years. I hope you find this material of interest and, more importantly, helpful in developing your machining skills.
anyway, enough of all that, so lets get one of the most basic procedures sorted.
SETTING THE CORRECT CENTRE HEIGHT FOR YOUR LATHE TOOLING
John has already shown various ways to do this operation, all good, but unfortunately things have changed over the last couple of years on the amateur machining front, and a new method was adopted by myself to cope with it, and it will be shown later on in the post why I went this way.
If I came to a lathe where I didn’t have any setup tools, I would use the old ruler trick.
Gently trap the ruler between the tip of the cutter and the job, and these are the results you will get.
click on image to enlarge
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- Cutter height is set too low
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- Cutter height is set too high
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- Cutter height now set correctly
Adjust the height of your cutter until the ruler is standing perfectly vertical, as in the last picture, and you won’t be far off correct for cutting.
As far as I am concerned, getting the right tool height is one of the most important parts when setting up for cutting.
This sketch shows what happens in the three modes you can be in.
NOW ON TO THE METHOD I NOW USE
The very first thing you need to do is to get a very sharp end facing tool to spot on centre height. The reason you do it on the end, is that it will allow you to set the cutter very low and it will still give a decent cut.
remember, you can see a larger image by clicking on each picture
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- Raise the cutter slightly, it does help if you use a QCTP, and you will see the pip in the centre getting smaller.
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- Carry on doing this in very gentle steps until you have it spot on centre.
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- If you go too high, drop the tool again and start from scratch. If you do this correctly, and get the height spot on, you will never have to do this again.
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- What is needed now is something that will stand on end and be very stable. I used an old home made DTI stand, but a piece of largish tube that has one end faced square, or even an old square could be used. I blued this up so that it could be seen better for this posting.
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- By resting this tool on your cleaned off cross slide, you should be able to swipe a line onto it by dragging it across your very carefully set tool. Make sure you keep it pushed down and steady as you do it. That is your setting tool made.
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- Now whenever you want to set the height of a tool or check one that is in say a tool holder, you just pop your setting tool onto the cross slide, and bring the tool so that the tip ‘splits the line’. For the average person, splitting the line should easily get you within 0.001” of the required height.
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- Now this bit will explain why I have gone to this method. A few replaceable tipped tools now come with a negative top rake. This is how the tool is supposed to be and is designed to work in that orientation.
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- Unfortunately this type of tool is very difficult to set up using the old techniques of height gauges etc. but the method described above overcomes this difficulty.
