Boring 4140 with HSS on a lathe

nerdyrcdriver · Apr 2, 2017

Hi everyone!

I am a student on an SAE Baja team at my college. I am running into trouble trying to bore a larger hole in a part made of 4140 on our bridgeport ezpath lathe. I got an awesome surface finish using recommended feeds and speeds and carbide tooling. But our only boring bar set (10 degree) uses HSS tooling. I have tried everything I can think of and have found online but the surface finish is always bad.

The best surface finish was at:
212 RPM (calculated to be 100sfpm)
.010" depth per pass
.001 IPR

I couldn't find any good videos on how to set up a boring bar correctly. I had the tool angled slightly upward just above the center of the part with a very slight angle on the tool post.

What could I do to improve? Are there any good resources online for how to set up a boring bar?

I feel like some how that I had the tool set up was causing more friction/ware instead of cutting action. No matter what I did it always screeched, though after some adjustment that came way down, but still not perfect.

plastikdreams · Apr 2, 2017

Try letting a machinist do it...Stick with the plastic and aluminum.

onecut · Apr 2, 2017

Boring with the Lathe | Smithy - AutoMate CNC - Machine Tools Check this out

keithmech · Apr 2, 2017

is the tool on centre?Did you check the hardness of the 4140 mat'l
Feed is on the slow side.Tool nose raduius?Tool stick out.how much is unsupported?What size hole? what size boring bar? coolant?
"good resources online".May start looking for a new career soon.They havebeen boring holes in stuff for along time and you cannot find info?wtf.
sorry for the pissyness but us old guys like to see alittle effort.

Lakeside53 · Apr 2, 2017

nerdyrcdriver said:
I feel like some how that I had the tool set up was causing more friction/ware instead of cutting action. No matter what I did it always screeched, though after some adjustment that came way down, but still not perfect.

What is your net relief angle on the nose?

Draw yourself a picture of a boring bar in a circle. You'll see that angling "up" may have created a rubbing point below the cutting surface. Try neutral.. and/or grind some more relief. Depending on the bore and bar size, you may also need to remove some of the bar "front" and underneath.

nerdyrcdriver · Apr 2, 2017

plastikdreams said:
Try letting a machinist do it...Stick with the plastic and aluminum.

What a great welcome to this wonderful community...

There is one machinist in the area and he helps us a lot, but he is always backlogged with weeks of work. He prefers to teach us a little and let us make our own mistakes in the learning process. When we run into real problems, he is extremely helpful. He is out of town on a personal matter now and I don't want to bother him in his limited time away from work.

If we just had professionals do everything for us, then there would be no point in building the car from scratch and competing, which defeats the entire purpose of the competition.

CarlBoyd · Apr 2, 2017

plastikdreams said:
Try letting a machinist do it...Stick with the plastic and aluminum.

Machinists regularly complain about engineers who know nothing about machining, and rightfully so.

But here we have a college student, almost certainly an engineering major, who is machining stuff, and asking questions. So rather than help him learn a little, you insult him. Bad idea

CarlBoyd

nerdyrcdriver · Apr 2, 2017

keithmech said:
is the tool on centre?Did you check the hardness of the 4140 mat'l
Feed is on the slow side.Tool nose raduius?Tool stick out.how much is unsupported?What size hole? what size boring bar? coolant?
"good resources online".May start looking for a new career soon.They havebeen boring holes in stuff for along time and you cannot find info?wtf.
sorry for the pissyness but us old guys like to see alittle effort.

No offense taken. I appreciate the help. I am not a machining student (they don't offer it here either). I know a lot more about milling than I do about turning. I'll try to tell you everything you asked about.

As in the post, tool is slightly above center, could easily be brought down.
I think the heel was clear from dragging, but I hadn't really thought about that when I set it up. No way to know now since we are required to remove tooling at the end of the day.

Starting ID of the hole is about 1.5 inches, desired ID is around 1.98. Final dimension is based on the bearing tolerance once it shows up. Just roughing for now.

Boring bar is an Everede 250 linked below. Specs are: 1/4in tool size, 3/4in bar diameter, 10in length. Original HSS inserts from the factory.

The bar was originally chosen by someone else that knows more than me, presumably because it fits the tool holder the best and is long enough to go all the way through the piece. Now the maximum length of cut into the part is 1.25 so I could easily go with a much smaller bar or shift the 250 back further in the holder.

Flood coolant, no noticeable heat is build up in the cutter or part at the end of each pass. I don't remember exactly what coolant solution we used. It is light blue when diluted into the correct amount of water.

I am an electrical engineering student that also happens to be interested in machining. Hobbyist level at best.
Maybe I just googled the wrong terms, but most of what I could find was setting up the geometry of boring heads in a mill.

This is the source that I used when trying to set up the boring bar.
Boring with the Lathe | Smithy - AutoMate CNC - Machine Tools

Tool
Everede 217 Product Catalog Production Style Boring Bars and Inserts

Thanks for the input guys!

nerdyrcdriver · Apr 2, 2017

CarlBoyd said:
Machinists regularly complain about engineers who know nothing about machining, and rightfully so.

But here we have a college student, almost certainly an engineering major, who is machining stuff, and asking questions. So rather than help him learn a little, you insult him. Bad idea

CarlBoyd

Thank you! I am in fact an electrical engineering student, but I have worked at a small engineering/production company that did a lot of machining. I regularly worked with the machinists to keep my designs (I do mechanical stuff too, it just isn't my major) easy and efficient for them to make with the tools we had on hand. That being said, I never actually gained any machining practice until this year. Mostly because I was the only one willing to read the entire manual for the cnc lathe we have and spent days cleaning it and making minor repairs.

I see a lot of stuff online about machinists hating engineers, and I do agree with some of it. Just like civil engineers hate architects. We just don't know enough about how the other group does things. I work with a lot of senior design teams to 3D print or machine parts for their projects and I often note that without 3D printing and disolvable support material there is no way their parts would ever be able to be manufactured.

Clive603 · Apr 2, 2017

Lakeside53 said:
Draw yourself a picture of a boring bar in a circle. You'll see that angling "up" may have created a rubbing point below the cutting surface. Try neutral.. and/or grind some more relief. Depending on the bore and bar size, you may also need to remove some of the bar "front" and underneath.

#2 on this.

Only way to see exactly how much clearance you have. But do draw the grind at the cutting point exactly as the tool is ground. Its very easy to end up with suitable clearance right below the cutting point only for the tool to touch a bit further down where the bore comes round. Front angle and radius at the cutting point are very important too. Again its very easy to produce a geometry which will give a bit of a push off and a bit of push down until stabilised by a moderate touch in the wrong place.

Although boring tools are inherently weaker due to the relatively long unsupported length making them prone to bend under cutting loads I'm no believer in setting up a bit to compensate for the bend. Adds another rather uncontrolled variable due to the change in cutting depth as / if the tool bends.

When your tooling starts mis-behaving for some unknown reason you need to control the operating parameters to get a handle to work with. Can help if you invert the tool and run it as an outside cutting tool to so you can see what its doing. Often the only way out of the box if you have done something daft which you don't realise or even don't know is daft. I'd say everyone here has done the daft thing at least once. Moi! I didn't count!

Clive

nerdyrcdriver · Apr 2, 2017

Lakeside53 said:
What is your net relief angle on the nose?

Draw yourself a picture of a boring bar in a circle. You'll see that angling "up" may have created a rubbing point below the cutting surface. Try neutral.. and/or grind some more relief. Depending on the bore and bar size, you may also need to remove some of the bar "front" and underneath.

I am not sure what the relief angle currently is. It has the stock inserts from the factory. We have most of the range of the 200 series 10 degree bars. Everede 217 Product Catalog Production Style Boring Bars and Inserts

Thinking back on it, I think the heel was clear of dragging but I can not be positive. There is always the possibility that I made a mistake that obvious and somehow didn't notice it.

nerdyrcdriver · Apr 2, 2017

Clive603 said:
#2 on this.

Only way to see exactly how much clearance you have. But do draw the grind at the cutting point exactly as the tool is ground. Its very easy to end up with suitable clearance right below the cutting point only for the tool to touch a bit further down where the bore comes round. Front angle and radius at the cutting point are very important too. Again its very easy to produce a geometry which will give a bit of a push off and a bit of push down until stabilised by a moderate touch in the wrong place.

Although boring tools are inherently weaker due to the relatively long unsupported length making them prone to bend under cutting loads I'm no believer in setting up a bit to compensate for the bend. Adds another rather uncontrolled variable due to the change in cutting depth as / if the tool bends.

When your tooling starts mis-behaving for some unknown reason you need to control the operating parameters to get a handle to work with. Can help if you invert the tool and run it as an outside cutting tool to so you can see what its doing. Often the only way out of the box if you have done something daft which you don't realise or even don't know is daft. I'd say everyone here has done the daft thing at least once. Moi! I didn't count!

Clive

Trying it on the outside could be very helpful. I will grab a scrap piece to play with the OD next time I am in the shop.

Thinking about it, I am starting to wonder if the HSS insert is supposed to be removed and ground before use. Right now they are kind of trapezoidal. The current shape is shown more clearly in the picture to the right, just above "Production Bars".
Everede 217 Product Catalog Production Style Boring Bars and Inserts

keithmech · Apr 2, 2017

If you checked that the bar is on centre and the tool is on centre,
I would have the bar sticking out of the tool holder only enough to go through the hole +1/8.As time is of no consequence slow down the rpm.
This will help keep an edge on the tool as you did not see how hard the mat'l is.4140 means very little on it's own.Kinda like 18 awg .

dgfoster · Apr 2, 2017

nerdyrcdriver said:
No offense taken. I appreciate the help. I am not a machining student (they don't offer it here either). I know a lot more about milling than I do about turning. I'll try to tell you everything you asked about.

As in the post, tool is slightly above center, could easily be brought down.
I think the heel was clear from dragging, but I hadn't really thought about that when I set it up. No way to know now since we are required to remove tooling at the end of the day.

Starting ID of the hole is about 1.5 inches, desired ID is around 1.98. Final dimension is based on the bearing tolerance once it shows up. Just roughing for now.

Boring bar is an Everede 250 linked below. Specs are: 1/4in tool size, 3/4in bar diameter, 10in length. Original HSS inserts from the factory.

The bar was originally chosen by someone else that knows more than me, presumably because it fits the tool holder the best and is long enough to go all the way through the piece. Now the maximum length of cut into the part is 1.25 so I could easily go with a much smaller bar or shift the 250 back further in the holder.

Flood coolant, no noticeable heat is build up in the cutter or part at the end of each pass. I don't remember exactly what coolant solution we used. It is light blue when diluted into the correct amount of water.

I am an electrical engineering student that also happens to be interested in machining. Hobbyist level at best.
Maybe I just googled the wrong terms, but most of what I could find was setting up the geometry of boring heads in a mill.

This is the source that I used when trying to set up the boring bar.
Boring with the Lathe | Smithy - AutoMate CNC - Machine Tools

Tool
Everede 217 Product Catalog Production Style Boring Bars and Inserts

Thanks for the input guys!

You probably know the general rule of reducing RPM and increasing feed to reduce chatter.
-Does a file cut the 4140 as easily as it cuts known "soft" steel? You may be cutting 4140 prehard. If so your SFM may be too high by a factor of 2 or so. Have you seen sparks while cutting? Is the cutting edge breaking down? I am suspicious that this may be central to your trouble.
-So, how deep is the hole?
-Is this insert sharp? Does it STAY sharp?
-Try painting the cutting edges and the bar itself with Sharpie to see where cutting is occuring and if there is rubbing
-How much stickout is the of the bar---try to minimize this so the tool just clears the hole.
-Increased clearance can be had by chanting the bar toward the cut 5 or 10 degrees.

Pictures of your setup, close ups of the inserts and bar itself post Sharpie and cutting might be a big help.
Cutting this hole with HSS should work!

Denis

PS The world would be a better place if more engineers had dirty hands.

Illinoyance · Apr 2, 2017

If you used an Everede bit right out of the box you are probably dealing with a negative lead angle. Assuming you are boring to a shoulder you will want to grind the bit so it has a zero lead angle when mounted in the bar. If it is a through hole you ban grind the bit for a positive lead angle.

Regardless of whether the bit is used or new you need to take it to the grinder to touch up the cutting face and the clearance angle. If you set up the bar so the bit has positive back rake you need to account for that when grinding the clearance angle.

onecut · Apr 2, 2017

Draw two lines to intersect "+"like take your tool out and place it in the cross to see what happens when you tilt it for your 10degrees-you will see the more you tilt it the more side rake your loosing.same if your tilting tool in the toolpost then your loosing front rake swinging the tool with reference to the cross will show you what your doing and where you need to grind your tool to clear the hole.Grind a small radius on your tool half your speed and take a trial cut if your happy leave it increase gradually untill your happy with the cuttings

plastikdreams · Apr 2, 2017

nerdyrcdriver said:
What a great welcome to this wonderful community...

There is one machinist in the area and he helps us a lot, but he is always backlogged with weeks of work. He prefers to teach us a little and let us make our own mistakes in the learning process. When we run into real problems, he is extremely helpful. He is out of town on a personal matter now and I don't want to bother him in his limited time away from work.

If we just had professionals do everything for us, then there would be no point in building the car from scratch and competing, which defeats the entire purpose of the competition.

Enjoy your stay...

CarlBoyd said:
Machinists regularly complain about engineers who know nothing about machining, and rightfully so.

But here we have a college student, almost certainly an engineering major, who is machining stuff, and asking questions. So rather than help him learn a little, you insult him. Bad idea

CarlBoyd

There's nothing worse for tooling and safety than an engineer trying to "learn" machining.

keithmech said:
is the tool on centre?Did you check the hardness of the 4140 mat'l
Feed is on the slow side.Tool nose raduius?Tool stick out.how much is unsupported?What size hole? what size boring bar? coolant?
"good resources online".May start looking for a new career soon.They havebeen boring holes in stuff for along time and you cannot find info?wtf.
sorry for the pissyness but us old guys like to see alittle effort.

I'm 35 but I still like to complain like I'm 70...Maybe it's a took maker thing?

APD · Apr 2, 2017

plastikdreams said:
Try letting a machinist do it...Stick with the plastic and aluminum.

So you must have been born a machinist that knows everything?

plastikdreams · Apr 2, 2017

APD said:
So you must have been born a machinist that knows everything?

I just might have been

72bwhite · Apr 2, 2017

There is a retired shop teacher who has a bunch of videos on how to machine
tubalcane or something like that. 10 to 1 he has one on boring.
people can describe it but nothing beats actually seeing it done.

funny but a very small change can make a huge difference in how it cuts
4140 even prehard will cut with hss it needs to be sharp and just don't spin it
fast

Boring 4140 with HSS on a lathe

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