Through-Coolant Hole Clogging

I am turning cast arylic. Specifically polymethyl methacrylate.

My .187" boring bar has a through coolant. With new machinery, I finally have the ability to us a through coolant. Haas lathe with their Bolt On Toolholder. Previously, I was shooting a flood coolant from the exterior of the hole, but not through coolant.

The through coolant hole is obviously very small. When turning acrylic, it’s not that uncommon for the material to melt if friction is high.

I’ve noticed that the through coolant hole can clog here and there with melted acrylic, or just get jammed with tine pieces of swarf that find it's way there, melted or not. I took a tiny tiny drill dit that's smaller than the hole and did my best to clear it out. Then also compressed air from both sides. It worked once, but the second time, I’m not having so much luck.

I am using a second method of shooting coolant through the tool block. So coolant is shooting from the tool block, and also through the boring bar. But I’m still getting some instances where I get clogs.

My thoughts….

1. Perhaps I’ll make the drill go deeper where I can, hopefully giving more clearance into the hole for boring. But I can’t always do this for every part, so this really is not the best solution.

2. I have another coolant outlet in the tool block. So I could shoot 2 sprays of coolant from 2 places in the block, as well as the boring bar through-hole.

3. However, is spraying coolant through the tool block a good idea at all? Maybe I shouldn’t use the coolant block nozzles at all? Maybe I should always have flow going in one direction from the boring bar out or the part, rather than from both the boring bar and also the coolant block. Coolant coming from 2 directions could keep the swarf from exiting the hole rather than keeping all coolant flowing in the same direction, being from the boring bar out the hole?

Any thoughts?

Thanks in advance.

Brian

How much coolant pressure do you have?

If you use both the large ports on the tool block, and the through tool, I suspect you won't have any through hole coolant. I assume you only have one coolant pump, so the large bore size of the tool block port would be the low resistance path for the coolant, and most of the coolant will go that way, starving the through tool.

For the through tool blockage, do you have filtration on your coolant? If you have plastic chips recirculating through the coolant, you might be blocking the bar from the upstream side of the boring bar, then the tool starves for coolant, and the hot acrylic fills the cutting end of the bar with melted plastic.

I would start by blocking any coolant that does not go through the tool. Right now you are splitting the coolant pressure with other ports- try putting all the coolant pressure through the boring bar and see if it's enough to keep the hole open.

edit: beat me to it adamm!

agree on filtration too, especially with plastics.

Yes, thanks.

I would prefer to have the only coolant being the through bar since flow would be in only one direction, but the hole is very very tiny on a .187" bar. I'm not sure that it would have enough flow to remove the chips quickly, and our programs running fast is imperative.

I am looking into the filter setup. It's a Haas ST10 which just arrived. I honestly don't know if it's filtered or where. I'll be looking into this...asking the rep now.

Thanks

OK thanks!

Agree with everyone above about filtering any coolant thru tooling, but don't go super fine on filters, you are only trying to keep fairly large particles out of your tooling.

A soft wire small enough to go thru your tooling can be turned into a flexible drill by cutting the lead end of the wire off on an angle with side cuts, then turning as you push it thru the coolant hole, especially on plastic.

bgray said:

I would prefer to have the only coolant being the through bar since flow would be in only one direction, but the hole is very very tiny on a .187" bar. I'm not sure that it would have enough flow to remove the chips quickly, and our programs running fast is imperative.

Click to expand...

The flow depends on the pressure at the entry to the tool, and the size and length of the hole in the tool. Smaller hole needs more pressure. Any leaks or other nozzles in the system will reduce the pressure and reduce the flow through the tool. I would start with sealing up the system, and make sure coolant ONLY comes out through the tool, then look at the stream and decide if that looks like enough coolant flow.

Rosedale filter bag.

Bag Filter Housing & Filter Strainers | Rosedale Products Inc.

bgray said:

and our programs running fast is imperative.

Click to expand...

Yeah, everyone wants fast, but in plastics, its often not the cutting speed that's the limiting factor in just how fast you can run but cooling and swaf control.

Rather than coolant, can you run a air blast? Reason is gases compress then expand, hence can for applications like this do a lot better at ejecting the swaf out the hole than a tiny hypodermic like coolant jet. Especially if you don't have really high pressure coolant and it sounds like you don't. A 100PSI air jet will expand a lot on leaving the bar, sure it won't remove the heat the same, but it may well get the swaf out the way so much better there's simply not the thermal issues to deal with. Equally for tools like that and especially cutting plastics, coolant filtration is a must, most plastics are a very similar density too coolant, hence easily wind up going around and around the system.

For what its worth i often end up running acrylic at steel like speeds, some times slower even. Only on things like external turning can you really hall ass. Way too many people look at plastics, see there soft and expect to run at alu like speeds or more and in some situations you can, but generally any hole like operation or tappng that never works that way.

The standard coolant pump only cranks like 25-35 psi (*) so it's probably just not enough to push the volume you need through that small coolant port. That is unless you purchased the "lathe high-pressure coolant" option, though it may still be inadequate. Using that coolant pump I rarely have good luck running coolant-thru with tools smaller than 1/4" myself.

*the pump doesn't have a rated pressure since all it does is push fluid, it's the job of the ports/nozzles to constrict and create pressure. I just don't want a smarty pants to correct my verbiage (lol)

2outof3 said:

Rosedale filter bag.

Bag Filter Housing & Filter Strainers | Rosedale Products Inc.

Click to expand...

+1

I picked up this on my local CL a little while back. Came with a stack of filter bags. Not sure what they go for, but it looked like it was worth the $300...

A few thoughts:

1) Always use tools dedicated to plastics, if the boring bar has been used on steel or Al it will dull and pick up material on the cutting edges. You want as close to a razor edge as possible with acrylic, with a small corner radius to help with finish. Be sure radius is sharp edged too, if honed in by hand (very fine diamond, no rocking).

2) Drill initial hole as large as possible, with just ~.005" remaining for bar, as deep as you can to prevent chip packing in hole. This is what's causing melting onto the tool tip, as long as you have even marginal coolant flow and a sharp tool, the only reason for melting is chips packed in the hole. A large hole cut deep minimizes risk. Just be sure the drill is fresh and cuts to size so a tiny amount is left for finish boring (one pass).

3) Tool clearances correct - you can run a lot of clearance angle with acrylic, and be sure to have the edge on centerline or very slightly above. Never have the tool edge lower than CL with PMMA, again, risk of friction and melting.

If you follow the three suggestions above you should have no trouble with melting while cutting.

guest said:

+1

I picked up this on my local CL a little while back. Came with a stack of filter bags. Not sure what they go for, but it looked like it was worth the $300...

Click to expand...

The bags of course go inside the canister. What is nice about them is you can pick the micron size of fabric bag holes. There is plenty of surface area to let coolant get through before clogging.

2outof3 said:

The bags of course go inside the canister. What is nice about them is you can pick the micron size of fabric bag holes. There is plenty of surface area to let coolant get through before clogging.

Click to expand...

Heh. He knows they go inside, his "what they go for" was referencing the new price, as he paid just $300 used.

Milland said:

Heh. He knows they go inside, his "what they go for" was referencing the new price, as he paid just $300 used.

Click to expand...

I must have been feeling a bit too literal yesterday.

About $1200.

Thanks everyone! Great info here!

YdnaD said:

...*the pump doesn't have a rated pressure since all it does is push fluid, it's the job of the ports/nozzles to constrict and create pressure. I just don't want a smarty pants to correct my verbiage (lol)

Click to expand...

Well I will be a smarty-pants.

All pumps are rated for a certain flow at a certain head. If the head is zero, you will get a rate of flow greater than the pump's rating. If the head is negative, the flow is even greater because pumps operate on differential pressure, and pressurizing the inlet will increase the flow.

Head can be converted to PSI by dividing feet by 2.31. A pump that is rated for say, 30GPM at 60 feet means if it lifts a 1 square inch column of liquid to 60 feet, it will flow at 30 GPM. 60 feet of head is equivalent to 26PSI. If the same pump only has to lift to 10 feet, the flow is greater than the 30GPM. Sometimes the pump manufacturers call it "head pressure", which just means they did the conversion for you.

23/46 Volt, 1 HP, 3 Phase, 345 RPM, Cast 83323 - MSC

Your city water comes in at a certain pressure. If you connect a garden hose to the spigot, it will spray a certain distance. If you put a nozzle on the hose to constrict the flow, the pressure will go up and it will spray a greater distance, but the volume will be less.

Same applies to the lathe. Constricting the flow will increase the pressure, and vice-versa. The OP needs more coolant pressure at the tool to clear the hole, so closing off the other coolant ports will increase the pressure of the coolant in his boring bar.

Well, the solution was very simple everyone!

The machine is brand new, and I haven't gone through a tank of coolant yet.

The coolant was low, giving me less flow.

However, my controller was telling me that I was still half full. So I checked, and part of the coiled wire attaching to the float was interfering with it. Reading accurately now.

Solved! But again, thanks for the great info.

Brian