Member postings for AdrianR

All my tests were with the spindle, Z and X all clamped down. Have not tried it with a loose spindle.

I have discounted a bent cutter as I have tried 4 different cutters, 3 of them were different makes, one was brand new out of the sealed box.

Also doing two spring passes removes the undercut, so the tool must be parallel and running true.

I think the most likely cause is head vibration, the cutter gets forced away from the work while in contact and then springs back between cuts. Which is why at high RPM it cuts true, it does not have time to move between cuts and the head deflection is averaged out.

I had a look with a magnifying glass and the undercut is not straight but convex which could also be explained by the above movement.

I have done some more tests.

I checked for the work moving, it is rock solid. I also put a digital level on the head and on the work while cutting. They did not move.

I tried a 16mm cutter and see similar undercutting.

I changed from the right to the left side of the vice. It still undercuts towards the vice. ie the direction is reversed.

I tried 0.25mm, 0.5mm and 1mm cuts all gave the same undercut.

I tried using the top of the cutter instead of the bottom (tip) and the undercut disappeared. For both the 16 and 12mm cutters.

I repeated the top and bottom of the cutter using an ER collet instead of R8 collet. It cut square at the top of the cutter, so the distance from the spindle is not the issue, but the length of the cutter is.

Over the 6mm height, the undercut is 0.15mm, if I do a 0.15mm cut on an undercut edge it cuts square.

All a big puzzle, I will carry on with what I am making and report back if I find any cause.

Hi,

I think I have the answer to why but just wanted to check my reasoning is right.

I was squaring the edges on a piece of EN32B 100mm square and 6mm thick. All went well and the finish was fine, then I noticed the edges were not square to the face. i.e. the 6mm edge to the 100mm face. I worked out the mill had undercut the sides at about 2 degrees.

The setup was. The piece was held in the vice on parallels with the working side to the right. This meant swarf was thrown backwards and conventional cuts were from front to back. The 12mm 4 flute cutter was in an R8 collet and was running at 800RPM. I was taking 0.4mm to 0.5mm conventional cuts.

I know my SX3 can cut square as I had just finished making some parallels and used the same setup to trim the ends. But that was using a 14mm cutter and running at 1600RPM.

I had used the speed indicated in Tubal Cain's Model Engineer's Handbook. Group D in table A on page 5.14 to find the 1600RPM. But I was not sure about running so fast and had calculated 800RPM from the 80ft/min figure given on page 5.15. I have since re-read and think I have too high RPM.

Feed was about 140mm/min.

I checked the head trimming, about 0.015mm over 200mm. I checked the surface of the parallels in the vice and they were similar. So the workpiece was flat and the head square.

Then to find the problem I tried squaring the end of a 40x6mm bar.

Same result;

• Using conventional or climb cuts.
• Using a brand new different make cutter.
• For 0.1mm cuts, and less undercut under this.
• Repeating the same cut without moving the X removed 1/2 of the slope. I.E only cut the top 3mm of the bar.
• To rule out the R8 collet I tried an ER collet, but the same result.

I then tried changing the speed, running it at 1600RPM I get square cuts even with a 0.5mm cut.

I can understand that a tool is pushed away on a deep cut and hence the need for a spring cut, what stumps me is the undercut.

My hypothesis is that the cutting edge first contacts at the bottom of the piece. Then as it rotates the cutting edge engages higher up, but at the same time, the tool/head flexes away. When the flute is passing the piece the tool springs back. This vibration of the head causes the sloping face.

Does this sound right?

Adrian

I have just started on making the simple rest too, good to hear it is rigid. I was a little worried if I had made the right choice. But I thought, my grinder has two wheels, I can always use it on the rough end and make an advanced rest for the fine end.

Adrian

Ah, this explains why a couple of my links disappeared recently. Sounds completely reasonable. I know of the product links on youtube, but must admit I take no notice of them myself. I will check before posting links in the future.

Adrian

I recently bought one from ARC, I am happy with it. A repeatable +/- 0.1 degree, if I need more accurate than that I would need to make an angle gauge or sine bar.

What a coincidence, This afternoon I started making my first pair following HH's book, then come in and see this thread for the first time.

Adrian

A thought. As central heating boilers became more efficient they had to have a fan to ensure a draft. If you cool your exhaust too much you too will need a fan.

Adrian

Dave, thanks for the reply.

Fascinating, I had not considered that level of measurement to check the operation of a clock.

Adrian

Dave,

If you are using a computer that has access to the internet you do not need GPS to have an accurate clock. With the NTP daemon running your clock will be synchronized within ms to UTC.

Adrian

What about a CBN wheel, wouldn't that be able to grind HSS and TC?

Adrian

Having just finished my very first attempt at carving, a love spoon as an anniversary present, I can vouch for the hardness of hornbeam. It started as a branch on my woodpile that was there for a couple of years, so was well seasoned and has come up with a great finish.

I have read when it is green it is easier to work.

Hmm, a wooden boiler, now that sounds like an interesting challenge, after all, you can boil water in a paper bag over a fire.

Adrian

I just googled it and found inkscape too **LINK**

I have to admit mine live in a draw under the vice. The advantage of a draw is it automatically sorts files so the most commonly used are at the front. I do worry about them getting knocked together, but I take care to not rattle them together too much.

One day I want to start a new draw, so I can have a set for ferrous and non-ferrous.

Adrian

When I was at school I had Miss Clarkson as my teacher. A woman who struck fear in all the kids. Tweed clad, Short, rotund with a mop of grey hair Einstien would have been proud of. To finish the image off, she had a witches wart complete with hair on her nose.

I had trouble remembering the trig formula until I made up Some Old Hag (Sin = Opposite/Hypotenuse) Can Always Help (Cos = Adjacent/Hypotenuse) To Oil Aircraft (Tan = Opposite/Adjacent).

I now look back on her with fondness, she went out of her way to get me into A level maths after failing my O level. She even gave me lunchtime lessons three days a week.

Adrian

I too am thinking of making an arbour, what is the best steel to use without hardening or grinding?

Adrian

Well the value 18.23 is right for 16.51 degrees but I don't think the angle is correct. I think it is 16 degrees 51 minutes which is 16.85 degrees. That would give 18.61 mm

Does anyone definitively know the angle as I have seen some other forums arguing what the angle is.

Adrian

What is the centre distance (hypotenuse) on your sine bar?

Adrian

I doubt you will have any luck with acetone if it is delrin as it is resistant to most common solvents. Nylon will dissolve very slowly in delrin. I would be tempted to try burning it off, then any char can be removed with a wire brush.

Adrian

What about diamond paper? **LINK**

Adrian