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I ran a test cut using a Best Carbide 3/8" 3F Carbide at 6750rpm, 81IPM (.004" IPT).75" DOC and .030" WOC (1.5" MRR) and worked my way up to .060" WOC (3.65" MRR) in .005" increments. The machine seemed quite happy at 3.65" MRR. I stand corrected. Apparently my weak spindle motor and sloppy gibbs were giving me the impression that the machine was tearing itself apart.
Awesome!
Here's the end mill I've been using a lot: https://www.ebay.com/itm/3-8-3-FLUTE...53.m2749.l2649
They are brittle, but they really cut nice and they last a long time, just don't drop them...
This conversation makes we want to try a four flute .5" and see what MRR I can get. I may run up against TTS but it's worth a shot!
Here’s a short video of the machine cutting 6061 aluminum at 3.65” MRR.
https://youtu.be/JPWGLqEtvl8
Hi Chris - The specific MMR is usually expressed as DOC/feed rate. In metric this is (mm depth of cut) / (mm/sec or mm/min) What are the units of your MMR ( inches?) So its the volume removed in time not just a distance? Peter
Hi Peter,
I mentioned the specifics up a few posts. This was 3.65 cubic inches per minute. 0.75” DOC, 0.060” WOC, 6750 rpm, 0.004” IPT.
Chris
Nice and quiet too!Quote:
Originally Posted by ChrisAttebery
https://i.imgur.com/LWRuEYM.gif
I’m making a solid tool post riser for my lathe. I couldn’t find a new piece of steel large enough at any of the local metal suppliers. I wound up buying a burn out that was approximately 35 lbs. On Saturday I spent a couple hours making chips and turned 14 lbs of steel into this:
https://uploads.tapatalk-cdn.com/202...0f877cb5ae.jpg
That was about half of the chips in the machine. Since then I’ve whittled another couple pounds off with the mill. I have to drill a few more holes and bore pockets for the hold down screws and this side is done.
https://uploads.tapatalk-cdn.com/202...b27e04e599.jpg
Sent from my iPhone using Tapatalk
A quick update: Since installing the 2hp motor I've been able to double the MRR on every one of my programs that I've run in aluminum to roughly 3" pre minute. I've done this mostly by increasing the WOC. I feel really comfortable with the machine running 81IPM (.004 IPT) with a 3 flute carbide end mill. The other day I was tweaking a program and had the feed override set to 150%. The mill powered right along at 120IPM and 4.5" MRR but the finish suffered a bit.
I got the flat parts of the new motor mount machined out of 1/2" 6061 last night. The inner pieces mount to the head and the outer pieces mount to the motor.
Attachment 445060
I went to make the round threaded spacers I need and realized that my 3/8-16 tap can't cut deep enough. :rolleyes:
I finished the mount up at lunch today.
Attachment 445062
Attachment 445064
Good news, good news, bad news...
The first good news is that I machined a bunch of parts yesterday morning and the mill is much more satisfying to run now that I've cranked up the metal removal rates.
The other good news is that the new spindle and gibbs showed up a couple weeks ago. I finally got around to installing the new spindle yesterday. It seems to have a bit better runout. I measured it at .0015" TIR roughly 1.25" from the end of the spindle with a 1/4" carbide shank in an R-8 end mill holder.
The bad news is that the ABEC 5 bearings that I installed in May are shot. The lower has a click and the upper feels like it's full of sand. :^( I ordered two sets of the cheap AC bearings from VXB that I had originally used. They should be here by the middle of the week.
Are you using strictly AC bearings or were those ABEC 5 units tapered?
I have found much better life with tapered bearings though I've been through loads of both, but I suppose there are number factors involved. Adding an oil drip to mine seems to have been a huge help in keeping the spindle nice and quiet. I'm using way oil from the automatic oiler and I just let it drip in the top of the spindle. It's not adding much oil, but I do find some oil running out the bottom "seal" after the spindle sits for a while. So there must be some purging action going on. Before I installed the oil drip I smoked the tapered bearings but had an important customer project at the time. So I pulled out some noisy bearings that I saved for just this scenario. After adding the oil drip and reinstalling the noisy bearings I started the spindle. It sounded like crap but I decided to stick it out, and I ordered two new sets of SKF tapered bearings. Well after about an hour of running those noisy bearings went quiet and I've been running them ever since. I have five months on them this year and an unknown amount of time on them before they got noisy and I removed them the first time. They are no-name Chinese bearings from eBay, $8 a piece. I have $80 of SKF bearings just sitting in my toolbox. So after this long story, I think lubrication is certainly the issue on these spindles. Though I do prefer the tapered bearings as they seem to require less adjustment.
These were ABEC 5 AC bearings from VXB. I pre-lubed them with Kluber Isoflex NBU 15. This is the same procedure I've used with the previous sets and those all lasted at least a couple years. I'm leaning towards too much pre-load or too much load from the heavier cuts I've been taking. I haven't used tapered bearings since I converted to belt drive 7-8 years ago.
The dynamic load rating of the compatible tapered bearing is more than twice that of the AC bearing (generally speaking as I'm not going to research all bearings). Too much load is too much load. Your finishes are beautiful and given your experience I am willing to bet you had the spindle setup just right, the bearings just don't seem up to the task (IMO).
I guess I'll try the AC bearings again and if it becomes an issue I can swap back to tapered rollers. It looks like the bottom bearing is rated to 6200rpm on grease though. I'd have to lower my upper RPM limit.Quote:
Originally Posted by CL_MotoTech
You have a one-shot oiler, switch to oil. There's a reason why bearings have higher RPM ratings with oil than grease (it doesn't matter if it's Kluber or cheap grease).
To add oil I made a plate that sits inside the mill head where the gear used to be, it has a compression fitting for the oil line, the oil literally drips from the fitting onto the top bearing and uses gravity to lube the bottom bearing. I'm using Vectra way oil. When the ways get oiled so does the spindle. The plate is glued in place with silicone sealer. Certainly a bit jenky, but trying to drill and tap holes down in there would be challenging and there's no reason the plate will ever need to come out. The plate has a hole that's slightly larger than the splined section of the spindle, which also helps to keep dirt and other things out of the spindle from the top side. The entire project took like 12 minutes. It's very simple but will get you to higher RPM and longer bearing life.
Good tip. I'd be worried about over oiling though.Quote:
Originally Posted by CL_MotoTech
Do you think that is an issue or does it just pee out the bottom once there's enough in there?
I can't switch to an oiled system. I cut a lot of plywood on my machine.
It dawned on me that I did recently cut a ton of steel at rates I wouldn't have attempted before. I wonder if that caused the bearings to go.
The Bridgeport J-head uses a total loss oiling system. Everything you put in at the top
eventually drips out the spindle nose.
I have read that they did made ones with sealed greased bearings for wood shops.