Super Noob question. First time milling

[Threadkiller]

Happy Thanksgiving everyone.

So quick backstory. I have zero, nada, less than no experience using a milling machine. I am really interested in machining so of course I wanted to get a mill; a Bridgeport namely. I ended up "settling" but not really settling since its an awesome little machine, on a Rong Fu RF-31 round column mill. The Bridgeport just wasnt in the cards at the moment financially and space wise. I am just super excited to finally have a machine. I got a good deal on it and it came with some accessories and "tooling" (parallels, collets, clamp kit, etc.) I put tooling in quotes because I did not have great luck with it this evening, my first time actually using the machine. The end mills that came with the machine are the typical Titanium nitride coated set of HSS 2 and 4 flute end mills that come in the wooden box. They seem fine for aluminum but once I broke out the steel they didnt seem too happy. I got quite a bit of chatter even taking small cuts ~.010. These end mills were used but extremely lightly so I think theyre still "sharp". Anyway, thats one little problem Im having but onto the real problem. I checked my machine and trammed in the vise and it all checks out within .002 on the Y full travel the length of the vise. I checked the top of the vise and the inside where you actually place your work. I was trying to mill a piece of flat steel bar I need to mill .25" off one side. So after multiple passes taking small cuts and getting tons of chatter I finally stopped as it was getting late and I dont want to wake up my wife since the chatter was so bad. Upon analyzing my passes its as if the flat bar was tilted in the vise on the Y axis. There is a visible slope between the milled surface and the hot rolled surface. After I saw that I pulled the bar out and measured, sure enough it is .015 bigger on one side than the other. I pulled my parallels out and checked them thinking maybe I grabbed two different sizes but no they check out. I guess its possible when I clamped the bar down that one of the parallels moved or something but I just wanted to check with the pros on here if theres any advice or anything to look out for other than what I mentioned. Again I couldnt keep going and try to figure it out since its late. Sorry for the extremely long winded post, just trying to go over everything. I think my first problem is I watch too much This Old Tony where he makes everything look super easy lol. Any advice, criticism or tips anyone wants to throw my way would be greatly appreciated.

 

[darkzero]

Congrats!

You didn't mention what size endmill & the spindle RPM you were running. Sounds like you may have been running them too fast. Some of those import box sets can be decent & some of them can be junk. I have a set but mine are uncoated. I don't use them often, they have worked fine for me, but I run them on the slow side compared to my higher quality end mills.

You mentioned hot rolled. Mill scale is tough on cutters. Try either grinding off the scale before milling or take a deep enough cut to hog through it if the dimensions allow.

 

[ttabbal]

It's possible that your work lifts in the vise. The amount being 0.015" would be a LOT. Use an indicator and verify the amount of lift. More than a couple of thou would be more than I would like. Tap it down with a dead blow hammer with a soft face. The parallels should be snug. Make sure you clamp in the center of the vise.

Look for some videos on squaring material. Using the mill finish as a reference is going to lead to bad parts. There are no guarantees that the surfaces are even close to straight. Making a block square to 0.005" or better is a great exercise for learning setups and cutting. It is also where many projects start.

 

[mikey]

I read your post several times and am having trouble sorting out what you're doing. You're trying to mill the side of a flat steel bar so I assume you mean a bar that is longer than it is wide and your cutting on one of the long sides, is that right? If so, in which direction was your table moving in relationship to the cutter? Was the table moving from right to left or left to right? Surprisingly, this matters. You might look up conventional vs climb milling.

What was your speed? Were you feeding manually or with power feed? If with power feed, any idea on the rate in inches per minute? All this matters, too. Mild steel has a cutting speed of about 100 SFM. For example, if you used a 1/2" diameter end mill then your rpm should be somewhere around 764 rpm. Were you going faster?

I have an RF-31 and it will go through mild steel bar with no problems. I use mostly Niagara Cutter end mills, though. If you could give us more details we might be of more use to you.

 

[darkzero]

I read your post several times and am trouble sorting out what you're doing.

Admittedly I just skimmed through it. I had trouble reading the post but it's late & my eyes are tired so I didn't try again. I probably shouldn't have even replied but when I saw the chatter part I immediately thought he may have been running the spindle too fast.

TK, not to criticize but it will help posting with paragraphs rather than one single long one. It's ok to make long posts with detail but it will make it a lot easier for the guys to help if we can read your post easier.

 

[mikey]

I read your post several times and am having trouble sorting out what you're doing.

Thanks, Will. I corrected my grammar.

 

[grzdomagala]

You definitely must do something about chatter - select correct spindle rpm, use cutting oil, maybe try another material (something of known quality - "scrapbinium" may be cheap, but has tendency to destroy tools) Heavy chatter may pull milling cutter from the spindle - even if the collet is tight - resulting in uneven depth of cut

Wysłane z mojego SM-N950F przy użyciu Tapatalka

 

[ThinWoodsman]

I dunno, maybe it's being run too fast, but it sounds an awul lot like workholding problems.
Gotta whack on the part with a hammer when seating, as ttabbal said.
Also the description of the setup sounds to me like a long bar sitting on parallels in the vise, with a few inches sticking out on either side. If that's the case, then the part will definitely move once the cutter gets to one edge. Need to put something under the parts that stick out from the vise, like a machinist jack or even just a bolt stuck into a t-nut.

 

[RobertB]

Holding hot rolled flat bar can be an adventure. It frequently is not flat across the wide side, being somewhat "cupped" and the edges are not square to the flats. This makes it move as you are clamping it down, As the others have pointed out, snug your vise up but don't crank down on it, tap the part down against the parallels with a hammer, tighten the vise firmly and then see if you can move your parallels. If they are loose repeat the above steps until the part is tight against them.

 

[ThinWoodsman]

It frequently is not flat across the wide side, being somewhat "cupped" and the edges are not square to the flats. ... As the others have pointed out, snug your vise up but don't crank down on it,

Ah, that makes me think of a couple other things as well. One would be to first square the sides that are going to be against the jaws of the vise for the main cut, using that trick where you put a ball bearing between the moving jaw and the part. The other is to run an indicator over the part before and after tightening the vise, to determine if you are overtightening the vise and bowing the part.