Horizontal mill: chip load and depth of cut

[Cortez]

Hi all. I am trying to understand horizontal milling a bit better. Until now I've just been guessing and adjusting until things feel/sound right but I'd like to have a better starting point. I'm sure this is detailed somewhere but I'm having a hard time finding it or maybe just understanding it.

First question. How do I know what Chip load should be with HSS horizontal cutters to determine feed rate? I read that manufacturers will provide this info but like many people, I have acquired my tooling second hand so this is unknown.

Second question: how do I know what depth of cut I can take?

Here's my current example, but I'd really like to know how to figure this out for any example:

Burke #4, 3/4hp, mild steel, 1/4"x2.75" cutter, 20 teeth, slotting down the middle of my part.

 

[benmychree]

The thing to do is find a slide rule speed/feed calculator, with one, you can integrate all the factors. With a small mill such as you have, I'd guess that feed/ chip thickness would likely be perhaps .002 per tooth, depth of cut will be limited by horsepower. Milling on on horizontal or vertical mills is really the same, except that horizontal mills likely use cutters with more teeth, but the factors/ rules are the same. Another factor is that feeds on small mills are likely to be in inches per revolution, on larger mills, mostly in inches per minute; the calculators allow for both types to be calculated.

 

[Cortez]

The thing to do is find a slide rule speed/feed calculator, with one, you can integrate all the factors. With a small mill such as you have, I'd guess that feed/ chip thickness would likely be perhaps .002 per tooth, depth of cut will be limited by horsepower. Milling on on horizontal or vertical mills is really the same, except that horizontal mills likely use cutters with more teeth, but the factors/ rules are the same. Another factor is that feeds on small mills are likely to be in inches per revolution, on larger mills, mostly in inches per minute; the calculators allow for both types to be calculatedso

Thanks!
Just so I understand. If I had unlimited machine horsepower, I could cut the horizontal cutter at a depth all the way until I hit the arbor - the limit is only my machines cutting power? That would explain why I couldn't find any rule of thumb on the max cutting depth...
Is it a correct assumption that feedrate should be halved for a stagger tooth cutter? So in my other example, I should treat my 20 tooth cutter like a 10 tooth cutter in the calculators you mentioned?

 

[francist]

I think John’s recommendation of a slide rule feed and speed calculator is probably the fastest and simplest way to go. I’m actually surprised that there are a fair number for sale on eBay right right now.

My suggestion was going to be if you get your hands on a copy of Moltrecht’s “Machine Shop Practise” Volume 2, he devotes quite a bit of space to calculating speeds, feeds, taking horsepower factors into account, machine efficiencies, etc. But, you have to do the calculations and they can get tedious. If you’re good with a spreadsheet you could probably generate your own calculator by working through his various steps but if one is already done then why bother. The book is an excellent read though with a lot of information and good illustrations for different operations and setups. Highly recommended. Machine Shop Practise, Volume 2, by Moltrecht.

-frank

 

[Cortez]

I think John’s recommendation of a slide rule feed and speed calculator is probably the fastest and simplest way to go. I’m actually surprised that there are a fair number for sale on eBay right right now.

My suggestion was going to be if you get your hands on a copy of Moltrecht’s “Machine Shop Practise” Volume 2, he devotes quite a bit of space to calculating speeds, feeds, taking horsepower factors into account, machine efficiencies, etc. But, you have to do the calculations and they can get tedious. If you’re good with a spreadsheet you could probably generate your own calculator by working through his various steps but if one is already done then why bother. The book is an excellent read though with a lot of information and good illustrations for different operations and setups. Highly recommended. Machine Shop Practise, Volume 2, by Moltrecht.

-frank

Thanks. I will look into getting a copy of that book and the slide rule.

 

[cwadej]

FSWizard app on your phone if you want the answers fast

 

[Cortez]

FSWizard app on your phone if you want the answers fast

Thanks. Do you know what tool I should use for the horizontal cutters? If I choose end mill, there's options like tool stick out that don't really apply for horizontals.

 

[cwadej]

I'd think endmill would be best. the engagement DOC tab seems to be more important for you.
i have zero experience with horizontal mill, thought the app might help.

 

[catsparadise]

Theory is fine, but practical experience may override this.

I have an Elliott model 00 mill and use the horizontal mode as much as the vertical spindle. Some practical advice based on this:
- When the cutter approaches the workpiece initially the cutter teeth bang into the work as the leading edge is vertical. I reduce the feed rate (I have a vfd to control the feed motor speed) until the bottom of the cutter is fully into the work. The feed rate can then be increased.
- The depth of cut depends on the rigidity of your machine. Mine has a single bar overarm support - about 2 1/2" dia - and will move with a too heavy cut!
- Obviously(?) the width of engagement with the work will reduce the depth of cut before chatter occurs
- Fast feed rate = poor surface finish, just like any machining operation
- Mount the cutter on the arbor as close to the spindle as is practical to minimise chatter, very important with a slab mill
- I generally run cutters at about 50 surface ft/min as I dont use flood coolant
- Make sure the cutters are sharp. I bought a tool & cutter grinder specifically to sharpen the used cutters that can be picked up cheap.

If you're a home gamer like me, time and productivity is less important than not wasting material and damaging your machines. Listen to what they're telling you, rather than being reliant on tables.

Hope this is useful, if not, please feel free to ignore or dislike it!

Rob