need bridgeport "basics" advice

Cardinal Knife

Cardinal Knife

Joined
Nov 25, 2007
Messages
340
okay so I tried doing the simplest of jobs today and wanted to drop some plunge holes into a 3/16 thick piece of 1075 and burnt up the mill. I switched out the mills slowed down my feed and lubed a bit with some WD40. Second hole worked okay but snapped off once I started moving left right to profile. I've tried searching milling 101, bridgeport basics, bridgport knee mill basics and I'm getting 130 page manuals and not much that covers basic procedures. Does anyone have any links or advice on mill selection, and speeds. I also can't figure out what RPM it's running at. The belt is in the second from top grooves. Our machinist gave us a basic setup years ago and that's where it's stayed. I'm not looking to do complicated stuff, just basics like milling guards and shoulders
 
Hi. This is my first post, and I'm not a pro, so I hope I'm not bending any forum rules.

There are two types of basic end mills, centering and non centering. Simply put, a centering end mill is capable of plunging due to way the end is ground, like a very shallow drill bit. A non centering end mill will not plunge very well at all, if at all. My guess based on your description of events, is that you have a non centering end mill.

1075 (unhardened I presume) should machine pretty easily. I'll also assume that you are using a tool 1/2" or less. That should be pretty flexible in spindle speed.

HSS or M42 (Cobalt) end mills should also give pretty good service, especially for the limited use you describe.

As far as speed and feed rates, I just checked and there are smartphone apps for apple and android for a couple bucks. Sounds like a good investment.

Your Bridgeport should have a legend on the side telling what speeds are. I will say that for years in the shop where I work, we ran everything on low speed because no one took the time to learn about what they were milling. We had virtually no problems with carbon steels, it just wasn't very fast.

Hope this helps.


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I would need to know a little more about what you were doing to be much help. What size endmill? Carbide or HSS? How was the endmill held? How was the knife held? How fast were you feeding when it broke? Were you climb milling?

You'll really need to figure out what RPM your running at, even for basic procedures, and wd40 is a poor machining fluid for anything but aluminum, which it's great for.
 
2 biggest killers in end mills on hand crank BP mills
wrong speed feed or depth of cut
slop in the table causing endmill to bite more then planned feed due to table slop (more so if climb milling )

makeing note if you are unsure of the term climb millling it really is time to click you tube and other info sources for milling basics
 
Hehe. One time I got a guy set up to knock some holes in some production parts when his machine was down. He comes and asks me to sharpen his drill, so I do. He comes back ranting about the drill I sharpened wouldn't cut, so I went back over and said show me. He flicks the switch down and grinds away on the part. But the head was in high gear, so turning the switch down ran the spindle counter clockwise. I sharpened the drill for him again.
 
Here, watch all of these videos with Eric Vaaler. Great basics, heavy on setup. Youtube is your friend here!
https://www.youtube.com/watch?v=T5gjkYvMg8A

Get a speeds and feeds chart- such as this, but they are all over the web-
http://www.sgstool.com/PDF-speedfeeds/SGS-Speeds-Feeds-GP.pdf

Learn how to calculate cutter speed based on RPM and circumference. After a while, you will be able to naturally dial speed in by feel and sound, looking at the chips, and more...

Get a copy of Machinery's Handbook. I believe some of the older editions are available in PDF form for free if you look around the web. Older copies are often better and more thorough as far as manual machine operation, and cutting theory. I'd find a paper copy if I was you though, you'll use it a lot by your machines.

As far as the machining you were attempting- a HSS center cutting endmill will remove material much more efficiently and aggressively when plunge cutting straight down, as opposed to slotting. You can't plunge a hole say 1/4" deep with a 1/4" endmill in mild steel, and then effectively mill sideways at full depth. You could with a very slow feed, but that could promote rubbing or work hardening in some materials and would be inefficient to boot.

Often I'll make a series of overlapping plunged holes at full depth, then slot that sideways when most of the material has already been removed. If you choose to slot back and forth from the start, you will have to plunge only 10- 60 thou deeper max in a lot of stuff before each pass, depending on the cutter. Pay attention to the feel of the table crank/handwheel as you turn it, you can feel when it's taking too much effort if the table is pretty free. Also with small cutters, shine strong light right at the operation, to watch the character of the chips (blue is not good most of the time) spray coolant when necessary, and watch the cutter for flex. Try not to re-cut your chips a lot, keeping the work blown free of chips with air nozzle/squeezy bulb or at least brushed off with an old toothbrush will extend your cutter life.

There's a whole lot more to it than that, but that's a general nudge in the right direction.
 
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Thanks for all the advice guys. I'll post a pic when I get to work to help visualize what I'm tying to do and show how it's clamped. The steel is from Admiral and I just went to their site and specs say hot rolled not annealed, so should I be annealing this stuff prior to mill or grinder??

>Tkroenlein- the mill was a centering mill and I think it was 1/4 or 3/8. Thanks for the app idea.
>Butcher Block- I don't remember how much lash is in the table but it's not too much. I know that's subjective so I can try to measure if it's important.
>Kuraki- I've seen the term climb milling but I don't know what it is.
>Salem- Thanks for all that I will check out the vids as soon as I get a chance. I was in fact attempting to slot with a 1/4" centering end mill, again, my ignorance on this subject is why I posted.

I have to get on the road... more when I get to work
 
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OK here goes I was hoping to do the plunge cuts to give me some even guard shoulders and if Lucky was going to mill off some of the bulk to reduce belt usage and time on the grinder obviously that did not go as planned I also understand my clamping situation is not optimal as I now see the blade is bowed and there's a gap between the MDF and the center of the blade.

Regarding play or lash if I turn the crank on the side to side table to zero I can move the handle to 25 before the table starts moving so I'm going to assume there's .025 lash??

The mill I snapped off was 3/16 HSS made in China the milI I burnt dropping down with the plunges was a centering mill HSS 1/4".

Excuse the grammar this was done speech to text


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Cardinal Knife said:
Thanks for all the advice guys. I'll post a pic when I get to work to help visualize what I'm tying to do and show how it's clamped.

The steel is from Admiral and I just went to their site and specs say hot rolled not annealed, so should I be annealing this stuff prior to mill or grinder??

>Tkroenlein- the mill was a centering mill and I think it was 1/4 or 3/8. Thanks for the app idea.
>Butcher Block- I don't remember how much lash is in the table but it's not too much. I know that's subjective so I can try to measure if it's important.
>Kuraki- I've seen the term climb milling but I don't know what it is.
>Salem- Thanks for all that I will check out the vids as soon as I get a chance. I was in fact attempting to slot with a 1/4" centering end mill, again, my ignorance on this subject is why I posted.

I have to get on the road... more when I get to work
Click to expand...

Yes


Re the mill

Find these videos

Darrell Holland/AGI Videos set of 5
https://www.hollandguns.com/

Bridgeport Mill - PMS - 3 DVD Set
http://www.precisionmeasure.com/brmill1.htm


They are worth watching, but they are very expensive to me.

Try requesting them from a library.
 
Maybe this just shows how big of a milling novice I am, but this is the first time I've seen step block/clamps used backwards. I guess there's more than one way to skin a cat. ;)
Erin
 
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OK I fixed the blocks mainly out of redemption, but I'm probably going to just stop at this point because I have no idea what I'm doing


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No big deal brother. Fixturing is an art. If your setup does what you need it to do, then it's not wrong... maybe just unorthodox. :D:thumbup:
Erin
 
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OK, I didn't feel like starting a new thread so just gonna post this question here. I normally do smaller knives with 1/8 stock so I usually hog off on the grinder. I pretty much used up a whole cut off wheel doing this blade what do you stock removal guys normally use a bandsaw or plasma cutter?


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