My first "milling"

WCraig

WCraig

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My alternative is to hacksaw and file but I made a DIY milling attachment for my little Atlas 618 lathe and all I need to do is cut a simple slot in a piece. I've watched quite a few Youtube videos but have no practical experience with any kind of milling machine. So I'd appreciate some step-by-step advice.

I want to make the slot in this:
Countershaft motor brace 9_121 WCT.cadx.jpg

I'm using this:

www.hobby-machinist.com

My DIY Atlas 618 milling attachment

Hey! I made diy milling attachment for my tiny Atlas 618 lathe!! I don't have a mill and acquiring one is not in the cards for the foreseeable future. But then I ran across Harold Hall's amazing website and the idea of using an angle plate to enable the compound to move a vise in the vertical...
www.hobby-machinist.com www.hobby-machinist.com

but I've gotten a proper milling cutter holder since that thread was posted. I'd intended to practise with some aluminum to get experience but need the steel part for an Atlas 10-F that I'm fixing.

The slot should be 5/16" wide and 2.25" from end to end in mild steel that is 0.200" thick. My thought is to drill 5/16" holes at either end. First, I'd planned to use my drill press, but the holes would be pretty precisely aligned if I do them with the lathe milling attachment. Any problems with that approach?

After drilling, I plan to switch to a 1/4" milling cutter. I have both 4-flute and 2-flute 1/4" end mills. Is the 4-flute preferred for faster cutting? The LittleMachineShop calculator says 1,380 RPM. Of course, I don't have power feed.

I'm thinking to start in the drilled hole at one end and slowly, using cutting oil, plow a full depth slot to the other end, down the middle. 5/16" minus 1/4" leaves 1/16" total or 1/32" on either side. So then I'll make a pass to mill the 1/32" off one side of the slot--conventional milling direction; not climb-milling. Finally cut the other 1/32" off the other side of the slot, again in conventional milling direction.

Are these cuts going to be too aggressive? I'm prepared to be patient and nibble away.

Any major red flags? I'm planning safety glasses and a face shield in case a cutter decides to become shrapnel!

Craig
 
Thats pretty much the way I'd do it in the mill Craig. A full depth cut might be pushing it though, I'd take two .1 depth cuts to waste the material away, then clean up the edges with a full depth cut.
Either cutters will work for this, but if your doing it in one pass without cleaning up the edges a 2 flute will cut closer to size and give a beter finish. When the four flute cutter has a flute at the end of the cut it deflects due to the load, that forces the counter clockwise flute into the side of the cut, making the slot slightly over sized and a rougher finish.
Did lots of milling on the lathe before I had a mill.

Greg
 
Nominal 1/4" cutter speed, HHS in steel is 900. Carbide will work at 1300, but that will smoke HSS. (Turn it blue and dull. )
 
A slower speed will give you more feedback as to how fast to feed the cutter into the workpiece. Speed charts are often intended for maximum production speed with very rigid machines. Smaller machines are more prone to chatter and breaking tooling if going too fast.
Also what Bredehoft said
 
markba633csi said:
A slower speed will give you more feedback as to how fast to feed the cutter into the workpiece. Speed charts are often intended for maximum production speed with very rigid machines. Smaller machines are more prone to chatter and breaking tooling if going too fast.
Also what Bredehoft said
Click to expand...
OK that makes sense. LMS recommends 80-100 fpm for HSS cutting low carbon steel. So for a 1/4" end mill, that's where their 1,380 RPM recommendation comes from. I can see how running at considerably slower RPM would be sensible for my less-than-perfectly rigid setup! ;)

Still don't quite follow about smoking the HSS cutter at 1,380 RPM. (LMS recommends 100 to 150 fpm for free-machining steel or circa 1,900 rpm.) I have trouble believing that they would set people up to destroy their end mills. I do note that they recommend much slower rates for stainless steel: 40 to 60 fpm. For carbide tooling, their suggested cutting speed is way higher--350 fpm for milling low carbon steel which equates to 5,350 RPM for a 1/4" carbide end mill!

Craig
 
You can try 1380 and see, it really depends on your machine and the quality of the cutter and hardness of the workpiece
One thing to be careful of is that the cutter doesn't grab the work and tear it out of the vise. Safer doing multiple passes when cutting a long slot like you described, and a slower spindle speed would be less dangerous in that regard. Fasten the work securely
M
ps I would probably screw the strip at both ends to a wood block, fasten the block in the vise, cut the slot, then cut off the end with the extra hole
 
Last edited:
markba633csi said:
You can try 1380 and see, it really depends on your machine and the quality of the cutter and hardness of the workpiece
One thing to be careful of is that the cutter doesn't grab the work and tear it out of the vise. Safer doing multiple passes when cutting a long slot like you described, and a slower spindle speed would be less dangerous in that regard. Fasten the work securely
M
ps I would probably screw the strip at both ends to a wood block, fasten the block in the vise, cut the slot, then cut off the end with the extra hole
Click to expand...
Ah, something more to worry about! ;)

I'll definitely start at slower RPM. I hear you on securing the work. I'll make sure the work is clamped as tight as I can get it. If the first piece, which is already cut to size, gets mangled then I'll try your idea of screwing to a backing piece of wood.

BTW, I'm pretty sure my material is 1018 hot rolled. I got it pretty recently in a proto box from OnlineMetal.

Thanks for the tips. Now I just need to get our taxes done* so I can have some time to play in the shop.

Craig
* We get to April 30 in Canada.
 
Craig, I would run your speed at about 600 - 800 rpm and take a full depth cut. Niagara Cutter suggests 80 sfm for HSS but this is on a big mill. For your set up, you just don't have the rigidity so I would cut the speed in half. Use a 2 flute cutter to reduce the amount of edge contact you have; chip clearance is not an issue with this cut. Use the upper part of the end mill to increase rigidity of the cutter and feed so you can feel a slight positive resistance to feed. Use cutting oil and you should do fine.
 
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