Fly Cutter

Project Proposal: Fly Cutter

It would be useful for us to have a fly cutter for the big Abene Mill for surfacing large workpieces. Currently we do not have any face mills that go much above about 50mm, and while it's possible to use the Boring head as a fly cutter, it lacks rigidity, which can make for a less than ideal surface finish.

Commercial options are well outside the budget for a makerspace, but it's possible to build one relatively affordably. I would like to propose that it would make a nice project for the members to build a fly cutter, and increase our machining capabilities.

Design options

There are multiple different styles of fly cutter design. Quinn Dunki of blondihacks, has a video series about a fly cutter build for her small bench top mill. This has a relatively small amount of mass, and the offset design can cause vibration at high RPM's it's ideal for relatively small mills. This old Tony has done something similar, but building it into an ISO 40 shank, rather than a straight shank Quinn uses. His is also larger for a large mill more akin to the Abene we have. It has all the same downsides, just at a bigger scale. An alternative design that doesn't have the imbalance issue, is that from Inheretance machining. This uses a large round slab of Aluminium as the body of the cutter. The Cutting is provided by a carbide insert, and there is a counter weight to maintain balance. It's quite a beast, and requires big machinery to make. We have big machinery. We could make one.

Materials costs

The abene mill uses an ISO40 taper fitting for tools, machining this from scratch while possible, is not a simple task as the taper needs to be exact, and getting a suitable material (such as 1.7227 / 42CrMoS4 / 4140 ) is going to not be cheap. Fortunately it's possible to buy a pre machined arbor with an ISO40 fitting on one side and a "soft" workable piece on the other side. One such item would be this one from scemama.ch which has a 50mm by 200mm shank that we would attach the fly cutter body to. The cost is 40chf, which is about €43 plus shipping.

For the main body, a peice of 30mm thick, 200mm diameter round 2011 aluminium from metalwinkelonline.nl is about €89.

The Inheritance machining design uses TPG-322 inserts. Which looks like a good choice. They can be had on aliexpress] for about €23 for 10.

All other parts would be relatively cheap, or could be found already in the metal stocks of the maker space.

To summarise the costs:

• ISO 40 Arbor - €43
• fly cutter body - €89
• Carbide inserts - €23
• Total cost ~ €158

Practical hurdles

200mm diameter is pretty much at the limit of what we can turn on the lathe, it is more than fits over the carriage, and it will require patience and skill to machine it, but it's doable.

Holding an ISO40 taper in the lathe so that we can machine it is going to require creative work holding. Not impossible, but not a beginner setup.

Project participants

This project is not really something one person can easily do in the space, it would be best with 3 or 4 people getting involved and working together, as well as contributing to the costs.