# DIY fly cutter for Sherline



## KKrum (Jan 6, 2022)

The Sherline 5000 mill spindle has a Morse #1 taper and 3/4-16 threads. The threads are used to mount Sherline's 3/8 end mill holder. They emphasize the importance of precision in these threads, so I don't want to damage them.

Would it be foolish to make a fly cutter that mounts to the threads? The closest I can single-point on my metric mini lathe would be 15.85 TPI. The spindle has about 4 turns of threads, so my threads would be about 0.0024 off over 4 turns. Would that risk damaging the spindle threads? What if I make the fly cutter body out of brass or aluminum so it deforms first?

Thanks!


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## mmcmdl (Jan 6, 2022)

KKrum said:


> Would it be foolish to make a fly cutter that mounts to the threads? The closest I can single-point on my metric mini lathe would be 15.85 TPI. The spindle has about 4 turns of threads, so my threads would be about 0.0024 off over 4 turns. Would that risk damaging the spindle threads? What if I make the fly cutter body out of brass or aluminum so it deforms first?



In a nutshell , would it be foolish ? YES ! Make a straight shank or just buy one . They're cheap and you wouldn't risk messing up your threads .


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## WobblyHand (Jan 6, 2022)

Sherline fly cutter is a really nice tool.  I got one for my PM25 mill.  Cuts very well and leaves a beautiful finish.  It's a perfect fit for your mill.


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## mikey (Jan 6, 2022)

I agree with using the Sherline inserted carbide flycutter, not just to avoid damaging the spindle threads with an improperly threaded device but also because it works better than any shop made fly cutter you might come up with. No offense intended but I've used them all on a Sherline 5400: HSS, brazed and inserted tip and there is no question that the inserted carbide fly cutter is the best choice for just about any material we commonly use in the shop. It can also cut ledges and that is a big deal. 

If you're concerned about banging on the drawbar to get a tool out of the morse taper, just thread a 3/4-16 nut on the spindle before mounting the fly cutter in the morse taper. When done, loosen the draw bar and thread the nut off against the fly cutter and it will pop out with no banging. 

The other option is to buy the straight shanked version of this fly cutter. It can be held in a tool holder or collet and will run accurately enough.


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## Aaron_W (Jan 6, 2022)

Third for the insert fly cutter, I even bought a second one with a straight shank to use with my Clausing.


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## KKrum (Jan 7, 2022)

WobblyHand said:


> Sherline fly cutter is a really nice tool.  I got one for my PM25 mill.  Cuts very well and leaves a beautiful finish.  It's a perfect fit for your mill.


Thanks for the advice. I've never been happy with the surface finish I'm getting from carbide insert tooling on my lathe, and I just reached a point where I started believing the guys who say small machines don't have the power for carbide. And I want to make a fly cutter, not buy one, just for the experience.

I found an item on Amazon that's similar to Sherline's #3051 MT1 blank, but a lot cheaper. The photos look like a nice ground finish. I'll test the fit in the spindle with dykem. If it's good, then instead of cutting it up, I'll use it as a master to set up my lathe and make something like Sherline's #3052 fly cutter.


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## mikey (Jan 7, 2022)

Most inserted carbide tools do not do that well on a Sherline machine but the flycutter is an exception. It can be run at high speeds and produces a superb finish. With aluminum, it is almost a mirror finish and is the best finish I have seen produced by a fly cutter of any kind on any mill. In steel, it is nearly as good.

Most of the time, I have no problem with guys experimenting and messing around but for this one tool I am strongly suggesting to you not to waste your time and money and just buy this one from Sherline. It is good enough that I bought and use one on my larger mill. Not many fly cutter work this well and can cut ledges.

Your call, of course.


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## KKrum (Jan 7, 2022)

Maybe I'll do both.


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## mikey (Jan 7, 2022)

Sure, it's your machine and it's fun to experiment and learn from your efforts. I did this and so have many others. I'm just telling you that I've used every kind of flycutter on the Sherline mill, including HSS, and nothing outlasts carbide or cuts nearly as well as this specific carbide tool. HSS can actually produce a nicer finish ... until it dulls in the middle of a cut and ruins the finish and dimensional accuracy of your part. I'm a HSS kind of guy except for this one tool, this flycutter.


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