Set screw holder with no flat? Safe???

mmurray70 · Nov 14, 2021

Ive seen few people on here in the past say they have run endmill holders with no flat on the tool. I havent been brave enough to try it, but im getting more and more sick of grinding flats on tools.

Did a little experiment tonight with a worn out 3/8 endmill. Clamped it on round shank and couldnt budge the tool with pair of vise grips. Tried clamping it much looser then I normally would and still couldnt budge it with vise grips. Holds way better then I would have thought.

Another thought, if a tool ever comes out of a collet it tends to PULL out, not spin. The flat does nothing (initially at least) to stop tool from pulling out which seems to be first sign of something comming loose.

Maybe this might be ok for smaller tools say 3/8 and under? Anybody here do this and get away with it?

wheels17 · Nov 14, 2021

If you raise a burr on the endmill, it can be extremely difficult to get the endmill out of the holder, and may damage the holder.

johneezreno · Nov 14, 2021

I've forgotten to put a flat on once and the tool worked it way out of the holder. Bad parts happened.

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boosted · Nov 15, 2021

Can't see any incentive to take that risk. Most tool manufacturers will just put a flat on the tool for you. Otherwise if you can't be bothered to grind one yourself, just switch to a steep collet, shrink fit, or hydraulic.

zero_divide · Nov 15, 2021

You normally need the notch if you are going to be running any roughing passes.
Because of the Helix Angle the tool will first spin slightly and then get pulled out as it slips. If you simply remove the spinning factor, it will be less likely to putt out.
Manufacturers usually grind the notch in such a way that the v shaped walls actually contact the screw, not the bottom. This way there is no up/down play possible.
I'd your notch is wider than the screw, pull on the tool as you tighten it.

Mtndew · Nov 15, 2021

mmurray70 said:
The flat does nothing (initially at least) to stop tool from pulling out which seems to be first sign of something comming loose.

You are 100% wrong.
The entire purpose of the flat is to prevent spin and pullout.
Look at weldon flats on end mills, notice the 45 deg sides of the flat?
Now notice how the set screw almost perfectly fits inside the 2 sides?

If you put flats on yourself, make them angled like a whistle notch so they can't pull out.

Or just continue to clamp on end mills without flats and hope nothing bad happens. :nutter:

dandrummerman21 · Nov 15, 2021

Do the rest of you who buy solid carbide endmills (like me 95%+ of the time) actually grind a flat on your tool?

Or do you take it to a green wheel on a pedestal/bench grinder, and just kinda make a "rounded flat-like mark" on the shank?

On a half inch tool, the "flat" might be .030" deep and kinda rounded in the middle, reminiscent of a whistle notch except the taper goes both ways.

Basically a long U shape (I don't know why i didn't describe it as such to begin with) a little bit wider than the tip of the set screw.

This takes me maybe 10 seconds at most, and I have a grinder set up right near where we put endmills in their holders.

I can't imagine being sick of doing it. Unless you take the time to put a proper flat on a surface grinder.

I did have one guy, though, who put a ~.010" deep flat along the WHOLE SHANK of the tool. When he'd put a rougher in like that and we'd do some high speed toolpaths, it would pull out on him. He's never allowed to do that again, I told him.

dandrummerman21 · Nov 15, 2021

Mtndew said:
You are 100% wrong.
The entire purpose of the flat is to prevent spin and pullout.
Look at weldon flats on end mills, notice the 45 deg sides of the flat?
Now notice how the set screw almost perfectly fits inside the 2 sides?

I don't buy carbide tools with flats, but I do notice this exact thing with HSS endmills (we've got a lot of 3/4 thru 1.5" hss) and the bigger endmill holders that come with em.

I would say, however, I'm a bit annoyed by a certain Detroit area toolholder maker. The set screws they use are a size down from what the "standard" should be, at least on sizes up to 3/4"

Like a lyndex 1/2" holder has, I believe, a 7/16-20 set screw on it. The detroit-area manufacturer I'm referencing uses a 3/8-24!

So if the standard flats on an endmill are designed for a 7/16, there'll be more play there.

Now, this doesn't matter to me as I don't buy small tools with flats, and make my own instead. But I do get annoyed that I have to use a smaller allen wrench, and I don't feel I get as much torque/holding power from the smaller screw. grrrr

Scottl · Nov 15, 2021

The flat doesn't have to be fancy. If grinding is too much of a PITA a few seconds with a diamond file will create an acceptable flat.

Always ask the lazy man for the quick and easy way to do it.

gregormarwick · Nov 15, 2021

I am always somewhat bemused by this kind of thread. You can't buy your endmills with flats on? I'm pretty sure about every single endmill I buy can be bought with or without a flat...

mmurray70 · Nov 15, 2021

Mtndew said:
You are 100% wrong.
The entire purpose of the flat is to prevent spin and pullout.

Im talking about a homemade flat, not factory weldon flat. I usually grind very small flat and make it little longer then needed in case i miss the perfect spot for height.

mmurray70 · Nov 15, 2021

dandrummerman21 said:
Do the rest of you who buy solid carbide endmills (like me 95%+ of the time) actually grind a flat on your tool?

Or do you take it to a green wheel on a pedestal/bench grinder, and just kinda make a "rounded flat-like mark" on the shank?

On a half inch tool, the "flat" might be .030" deep and kinda rounded in the middle, reminiscent of a whistle notch except the taper goes both ways.

Basically a long U shape (I don't know why i didn't describe it as such to begin with) a little bit wider than the tip of the set screw.

Exactly. This is what ive been doing too and I hate it. Green wheel dust going everywhere. Never perfectly consistent. What if taper isnt in perfect spot and you acidentally clamp on the downhill part?

I do tend to make my flats longer like the guy you mentioned. Never had one come loose yet, but i usually use 3/8 tools so no crazy forces.

e30ryan · Nov 15, 2021

I prefer to buy my endmills without flats and then add them myself (5 seconds on a green wheel). This way I can control the exact amount of stickout I want for the particular application.

kustomizer · Nov 15, 2021

e30ryan said:
I prefer to buy my endmills without flats and then add them myself (5 seconds on a green wheel). This way I can control the exact amount of stickout I want for the particular application.

I haven't had any trouble with the smaller tools moving, flat or not 1/8 and under so I don't bother with them but 3/16 and up get flats. I find the weldon flats are in the wrong place for me many times especially on the 3/8 with 3/4 OLC, I need just a bit more stickout, so I grind lots of flats

Mtndew · Nov 15, 2021

dandrummerman21 said:
So if the standard flats on an endmill are designed for a 7/16, there'll be more play there.

I think I know what mfg you're talking about.
As for the flats being wider than the screw, this shouldn't matter as long as you're pulling the end mill down into the holder as you tighten the screw.
But I agree, it should be a larger screw.

MCritchley · Nov 15, 2021

As others have said, just grind an 1/8” wide flat just where you want it. You will have a lot more contact that without. Will an endmill without a flat run for hours in a chatter cut loosen?

A properly equipped shop should have a mounted diamond wheel ready for a job like this. A one minute trip to the grinder and your finished.

kenton · Nov 15, 2021

Well I'll admit to being the black sheep. I very seldom grind a flat on a tool without a weldon flat. The first shop I worked in the manager saw me putting flats on the tools and told me I was wasting time. "If your set screw is tight you won't have any issues" he said. And that has mostly been true. Granted that shop was all 40 taper Haas mills and high speed machining was not part of their repertoire. Additionally, nothing was programed to push the limits of the machine unless the machinist took it upon themselves to bump up speeds and feeds or reduce the number of step down passes. The other possible saving grace was we mostly ran 1/2" and smaller tools, and the larger roughing endmills were mostly HSS corncob roughers that already had flats on them.

In the shop I currently work in I still don't grind any flats. Granted I run a rather wimpy 40 taper open cell CNC doing prototyping work, but I haven't had any issues with tools pulling out, even with 3/4 carbide endmills.

Vancbiker · Nov 15, 2021

You’re not the only black sheep. I don’t grind flats on round shank tools either. I use up to 3/4 diameter on my 30 taper Mori in aluminum. Been doing that for 9 years now and never had a tool move yet.

If I was running a more powerful machine or cutting something harder than shiny plastic that pretends to be metal, I’d be doing flats.

mmurray70 · Nov 15, 2021

I knew there was some guys out there that did this! Thanks for coming forward lol.

I might just give it a shot on next inexpensive job, worst thing could happen is bust a tool I guess. Im drawing line at 3/8 though. These are my go to roughers. 1/2" and up tools are so expensive these days it wouldnt be worth the risk. I just hate grinding anything in my shop so if I can avoid the time, mess, dust, and fiddling around with stickout it would be awesome.

metal-ica · Nov 15, 2021

I don't grind flats (or wear condoms).

Most of my roughers are 1/4 shank with smaller tool diameters and run them up to 15k rpms.

If I'm heavy roughing with 3/8+ I'll grind a flat but I still finish with flat-less 1/2" end mills all day.

Set screw holder with no flat? Safe???

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