Re: Increasing Motor RPM via VFD
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Get some experience under your belt and then you can decide if things need changing and what bit is best.
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Brian,
Not having a reference or working experience makes it difficult to determine what you is good or not. Buying used machine with used bits (previous owner had a small business) another uncertainty. I do know that plunging as you said and cleaning after sounds like a lot faster than my current experience of side to side slitting in small steps.
Imran? On Jan 30, 2021, at 12:41 PM, Brian Lamb < blamb11@...> wrote: ? I don¡¯t know that end mills will be any different in depth of cut on side to side passes, but they will plunge better than a birdsmouth bit. I¡¯ve done mortises where you plunge 2¡± deep, step over 1/2 the diameter of the cutter, do it again, then when the whole mortise is plunged, finish it side to side at about 1¡± depth per pass, that¡¯s with a 1/2¡± cutter.
You will get clean bottoms with either cutter, no difference there as long as you are sliding side to side at the bottom.?
Sharpening? How many thousands of mortises do you intend to do? Even a cheap HSS end mill should cut close to a thousand mortises before it gets dull¡ that would be a lifetime of mortises for me.
Brian,
My results were fine with 14mm in Cypress but I took small steps. If endmill won¡¯t allow a bigger step (depth of cut per pass) then i have no interest unless it was cheaper and bits would last longer. I don¡¯t know if end mills can be sharpened but no luck finding anyone to sharpen birdsmouth.
The previous owner demo in hard maple was not good. I don¡¯t plan to get carbide but wanted to compare apples to apples.?
20mm birdsmouth in HSS is still over $100.
Lastly, my perception is that i will get clean bottom holes with end mills. Not sure if that is true.
Imran On Jan 30, 2021, at 11:41 AM, Brian Lamb < blamb11@...> wrote: ? Are your existing results bad? I doubt it. I wouldn¡¯t spend the money on carbide for the occasional mortise¡ a 3/4¡± carbide extended length end mill will set you back north of $100 and carbide is pretty easy to snap off, especially on these comparatively flexible and rickety machines we are talking about. It would be a different story on a 10,000lb machining center.
Your best bet for 3/4¡± mortises would be an extended length HSS or Cobalt end mill. 4 flute would be stiffer, but because of less room for chip evacuation, it will tend to burn more, so I¡¯d probably try a 2 flute version¡ stiffness in wood isn¡¯t the big issue anyway.
I just want to try and see if better results can be had. Jonathan mentioned center cutting, 4 flute end mills. Does anyone have a recommendation for 3/4¡± end mill? Felder supplied birds mouth is 100mm long for 20mm.
Generic end mills may be more affordable as well. Felder 18mm HW is $150.
Imran?
On Jan 30, 2021, at 11:07 AM, Brian Lamb < blamb11@...> wrote: ? VFD rated motors can generally run up to 200hz, CNC router motors up to 400hz. Torque does drop dramatically over about 90hz.?
OK, I¡¯ll probably start a war¡ but you don¡¯t need huge rpm on router bits or on these mortisers. You can¡¯t manually move the cutters at a rate that justifies all this rpm, all you will get is burning. Now, on a CNC router, different story, it has the capability to move the cutters at 500-1000ipm and can make use of all that rpm. I have machined mortises on my old Deckel mill and routinely done them at 1200 rpm and they come out great.?
On Jan 30, 2021, at 7:54 AM, David Kumm < davekumm@...> wrote:
Given the FD is direct drive, I would think the speed is closer to 3400 in the 60 hz market.? Generally you can overspeed a 2 pole motor to about 90 hz assuming the motor is decent quality.? Downside is that torque will be reduced because you aren't maintaining the volts/hz ratio.? The benefit and need for higher speed is really for small diameter bits so the reduction in torque might not be a big deal.? 5/8" bits are not a great choice for more speed and less torque.
4 pole or 6 pole motors are good for higher hz and vector duty motors are good for something like 5000-6000 rpm or up to 240 hz.? When you do that you usually oversize the motor to compensate for the loss of torque on the high end.? You also need to realize you may have way more torque on the low end than what the machine is designed for so care must be taken.??
Thank?Brian for straightening me out on this years ago when we had a discussion here about Rong Fu mills.? Dave
After realizing that people have used end mills on their mortising attachment, I was curious if there is a way to increase the RPM of FD250. The bit on morticing attachment is likely running around 5000 RPM, whereas FD250 is around 3000 RPM.
This article says it can be done as long as motor does not exceed it¡¯s FLA, is not electrically overloaded and operating with it¡¯s mechanical design limits.
Anyone got an idea how much more speed might be possible?
Electrical parts can be measured but I have no clue on mechanical side of what margin might exist.
This may not result in anything meaningful but I like to learn. One thing leads to another ....
Imran
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