Advise on BP end mill size.

Good morning..

I apologize in advance as I have not searching thoroughly past posts, if this topic has been discussed previously at length as have very limited bandwidth where I am at. More than likely wont check back for several days.

Have not done much milling on my 2Hp Bridgport and still getting the feel of it. The little I have done have chipped a couple of HSS end mills and turned out decent work pieces but am running low on the few end mills that came with the BP.

Time to purchase more cutters. Will price South Africa but more than likely buy in USA as my wife is currently visiting for Thanksgiving. So far have been machining cast iron, mild steel and EN8 Steel. Have a few SS jobs in the pipeline.

I have metric R8 collets but no R8 weldon endmill holders, so will be buying these. An ER collet system I will purchase at a later date when I use the mill more frequently not sure on the size. Majority of my drills and endmills I have are metric.

Q1- What would be the ideal size and flute end mill to buy for this machine for the above materials I am planning to mill? Do i go shotgun approach and get like 10 of each from 4mm- 20mm? I know it depends on what the job is, but that is the unknown. Never know whats gonna break and needs repair or make a new part.
Q2- What are the most common sizes you guys normally use?
Q3- Carbide vs HSS? A fellow PM was selling some 9/16 carbide mills for $7 ea which sounds fantastic from here esp when I purchased a dormer 6mm carbide end mill for some bennex plate for $136 USD!!
Q4- Do i get some insert mills? 1/2", 3/4"?
Q5- If fellow PMs dont have any for sale how to detect which ones to purchase on ebay or Amazon?
Q6- Was going to buy a bunch of inserts for the lathe tools but see prices on ebay all over. If sticking with brand names are they fake, who are decent sellers to purchase from and how much should I pay for say CNMG, TNMG & WMNG etc? (16mm and 20mm tool holders)

Basically just wanting a good supply of the most common mills I need.
There is a company in SA selling resharpened HSS end mills but last I checked their prices where close to new price, so stayed away.
Last lot of carbide inserts I bought a few years back from SA were Korloy and they hold up well.
Thanks in advance and appreciate the valuable input.

Cheers, Greg

zimbo said:

...how to detect which ones to purchase on ebay or Amazon?

Click to expand...

Hopefully you will have plenty of response to the other questions. I'll address just the one, Amazon first.

Mostly, I just don't. They pop-up so annoyingly much when doing a search, I return the favour and USE THEM for further searching so as to buy from ABA... Anyone BUT Amazon. Your Mileage May vary.

As to eBay? You have greater risks where you are than I do here.

Even so, it has long been a reducer of risk to go and see "other items", and "visit our store", then track off of those to until you find a brick-and-mortar enterprise UNDER that eBay blanket that has its own verifiable history.

There are plenty of long-established and well-regarded firms that have simply ADDED ebay presence and still do the bulk of their business by traditional channels. They are very rarely "the cheapest". Also very rarely any trouble.


WHEN .. you are looking at a Criterion boring head on R8 ass-muscle AND the other "products" the vendor has for sale are used Lebanese tennis shoes, Chinese VFD, and kid's toys?

Just go and use a different loo. Your ass will thank you.

I do the vast amount of my work with 1/2", 3/8" and 1/4" end mills. I haven't touched my fly cutter in years and use the boring head if I need a specific radius.

I don't remember who, but one member made a pretty compelling argument to avoid cutters larger than 1/2" whenever possible. In solid carbide those cutters are fairly reasonable, very stiff and available in a huge variety of grinds/lengths/coatings/ etc.

Were I in your shoes, I'd stock up on a few of each of these- Single End Variable Flute End Mills - MariTool

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I would suggest getting a few cobalt roughing mills, in 1/2", 5/8", and 3/4" or the metric equivalents if that is what you have collets for. If you are doing steels, especially stainless, I suggest a FINE tooth rougher. These end mills use much less horsepower to do a cut compared with a standard end mill. They make fine chips which are easy to vacuum up. The downside is that the edges of the cut will have a slightly corrugated surface. If you rough about .025" undersize (leaving .025" material to still remove), then a final pass with a conventional end mill will yield a smooth surface. Cobalt is much tougher than carbide and more tolerant of mistakes, yet still stays sharp in difficult materials.

Another suggestion, if you have not already made this a standard practice, is to NEVER climb mill in steels. ALWAYS mill in the conventional direction, which will not allow the endmill to grab the material and pull itself into the cut (climb). Although climb milling can give a smoother cut, on an older manual machine like a bridgeport, the gibs and the leadscrew have enough play that a climbing cutter can yank the table and work piece into the tool, dramatically increasing the depth of cutter engagement instantly. This leads to pulled out work pieces, broken tools, and all sorts of damage, potentially even to you too. The exception to the NEVER climb mill recommendation is with small skim cuts to hit a final dimension. In this case, the cutter is removing less than (for the sake of argument) 0.025" of material. In this case, the chance of grabbing the work piece is lowered. A good practice is to tighten the lock on whichever axis is being moved so there is some drag, and to lock the stationary axis. Feeding more slowly will also provide a margin against disaster. Observe traditional feeds and speeds with a manual tool. A CNC can operate in a much different speed/feed regime with rigid ways, tight leadscrews, carbide cutters, computer toolpaths, and flood coolant. You DO NOT want to try to copy their performance on a Bridgeport.

Finally, my advice is to avoid 2 flute cutters generally in steels. With a bridgeport, keeping the amount of material removed per tooth low and minimizing the odds on the tool suddenly grabbing a big hunk of material (always a concern when manually feeding) are enhanced with a 4 flute cutter. I only use 4 flute cutters when I am doing steels. There are advanced geometries with varying helix angles, both in roughing and regular end mills, but I have not tried them. I use 4 flute carbide cutters in steels mostly, but given their expense and difficulty of running down to the tool store for a replacement where you are, either HSS or cobalt would work fine. If you keep the feeds and speeds right, use some lubricant, and make sure the work piece is RIGIDLY held, the gibs are adjusted, and the cutter diameter and stickout are well thought out, you should get very good tool lifetime. 4 flute cutters often are not center cutting, and thus cannot plunge without a center hole being drilled first, but you CAN obtain center cutting end mills. You just have to specify them. Looking at the bottom of the end mill the difference is usually pretty obvious. The center cutting end mills have a longer flute on the bottom which extends to the center of the tool. Non center cutting end mills have equal flute length on the bottom and do not extend to the center.

I mentioned 1/2", 5/8", and 3/4" cutters. Smaller cutters are ok too, of course, but they become increasingly fragile as the diameter decreases. The rotational speed will need to go up, and it is important to keep in mind the depth of cut and chip clearance. A small cutter will snap much more easily than a bigger cutter generally. If the cutter does not sound and feel "happy", stop immediately and try to understand why. This is why I really like roughing cutters on a manual machine. You can turn the speed up, and they just plow through steel like butter. You have to be REASONABLE of course, but they will remove a lot of material quickly, and usually without drama. If milling steel for welding, the corrugated surface is often irrelevant.

I hope this helps. Best wishes for success in you endeavors!

Michael

zimbo said:

Q3- Carbide vs HSS? A fellow PM was selling some 9/16 carbide mills for $7 ea which sounds fantastic from here esp when I purchased a dormer 6mm carbide end mill for some bennex plate for $136 USD!!

Cheers, Greg

Click to expand...

Just to clarify, those cutters were 9/32", not 9/16" (that would indeed be a good deal) https://www.practicalmachinist.com/...16-shank-carbide-endmills-355662/#post3246842

Still have some if anyone wants, just wanted to be clear on the size...

My current workhorse is .375 4 flute uncoated carbide. 95% of what I do is 2024 aluminum so they last a good amount of time. I only really step up to larger cutters when I am side milling. I do have some .375 and .3125 firex coated cutters, but I reserve them for the tool steels.

Evening Guys,

All thank you very much for the detailed advise. Will take it as gospel and start the buying process and compare the prices between USA and SA and buy through legit companies.
LOL, already found out the hard way about climb milling
Final Question... whether carbide, HSS or Cobalt cutters can you cut the full dia of the cutter or just half or 1/3 of the diameter. I read somewhere a while ago, maybe Harold Hall book to take 1/3s?

Cheers,
Greg

Hello Greg,
My perspective on your question about width of cut is that it all depends. If you are cutting a slot, sometimes you have little choice. If you are facing a flat part, then you DO have a choice. In either of the cases above, the determining factor is the depth of cut and chip clearance. If you are milling the edge of something and trying for maximum material removal, full engagement combined with a deep cut is not usually going to work out all that well. Being the sort who struggles sometimes to be patient, I resort to roughing end mills whenever possible. They can really speed up work on a Bridgeport. If you combine a rougher with the same diameter 4 flute (the helix angles are different for different types of materials, so buy for the material you are machining most) finishing end mill, and assuming your finish dimension is referenced to the cutter diameter, either the edge or the center, then simply replacing the rougher with the finish end mill gives you the final dimension you want, without too much arithmetic.

I would be wary of blindly following advice from a book about the cutter depth radially. Bridgeports are not terribly rigid, and the backlash and slop in the ways will have an effect on the stability of the cut. Also, you are limited by horsepower and RPM. My philosophy is to be conservative and gradually become comfortable with what your tool can do. I prefer larger diameter end mills when possible, as the stiffness goes up as the diameter cubed, and I find them to be more durable than smaller tools run at a higher speed. Others probably will disagree with this. It is really a personal choice which only experience can inform. So with respect to the radial engagement, consider the axial depth and take it easy at first. After a bit you will have a good idea of what you can get away with in the materials and geometries you machine. Also, avoid the temptation to use a long endmill when a short one will do. If you run a lot of parts which can get by with a small Length of Cutter, get end mills like that. The additional stiffness will really matter.Just keep in mind you have a fairly flexible machine, 3000 RPM or so maximum rotational speed, and only 2 HP maximum. A Bridgeport is NOT a heavy duty CNC mill! So patience can be a virtue. Wish I had some...

All the best,
Michael

I personally prefer 3/8" 4 flute roughers for slotting or pocketing. On my mill I start having rigidity issues and have to take baby cuts when slotting much over 1/2". For side cutting I can see the advantages a larger cutter would have.

Kenton,
I agree if the slot is small. I have been plunging with center cutting 4 flute carbide endmills to remove most of the material in slots in recent times. If the overlap isn't too big, say 50% or less, then the remaining scalloped slot edges clean up very easily and quickly with a full depth roughing end mill. A finishing end mill cleans up the slot to final dimension. The plunging cuts seem to be easier than milling slot lengthwise deep in a pocket with full cutter diameter. I do like the roughing cutters in any case!
Michael