Cutting Parameters for Small Slotdrill

[Chris Evans 6Participant @chrisevans6]

It is only in recent years (last15) that I have used carbide cutters on a pantograph. Prior to that they where a bit pricey for the small companies I worked for. And yes 18,000 was about as quick as they would go. On retiring I was offered for free a Deckle "KF12" one to one /ten to one ratio machine. Space and justifying how much use it would get stopped me accepting.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by JasonB on 16/03/2020 13:13:07:

Would the old pantographs have been using HSS so needed slower speeds than Andrews Carbide?

[…]

.

Yes the old pantographs used HSS … or perhaps more correctly, whatever special grade of steel Taylor Hobson specified.

But the current range [see my earlier link] includes carbide versions ; and the machines haven’t changed much.

MichaelG.

[BazyleParticipant @bazyle]

Off at an angle have you considered roughing it out and adapting some kind of spark erosion for the final detail. I imagine you could use a very small point for fine detail. It would take longer but if it is CNC you can just leave it to get on with the job while you have a cup of tea, or perhaps a plantation of tea.

[Anonymous]

I've bought a 0.5mm slot drill; good grief it's tiddly widdly. I had trouble seeing the cutting edges even with a magnifying glass. So it's time to make some decisions on feeds and cuts.

Andrew

[Anonymous]

I finally got around to machining the cover plate for my traction engine regulator. It took some experimentation, and broken cutters, to get a result. I started with two 0.5mm 2-flute cutters from Drill Service, albeit their economy range. In all cases the cutter was running at 24000rpm. I started with a stepdown of 0.1mm and stepover of 75% and a feedrate of 80mm/min. The cutter started well but broke about half way through a 2 hour program. With the second cutter I dropped the stepdown to 0.063mm and the feedrate to 40mm/min. The cutter finished the initial machining but broke at an undetermined point. The finish left was poor with ridges and uneven surfaces.

I then bought two 0.5mm 3-flute K2 carbide cutters from Cutwel. After machining the basic outline the original program cuts the centres of the O and P. These are very small openings, not much bigger than the cutter. I was concerned about stiction on the table possibly overloading the cutter. So I changed the program to remove them, changed the stepdown to 0.05mm, the stepover to 60% and increased the feedrate to 120mm/min. The program took just under 2 hours and ran to completion without breaking the cutter:

I then ran a separate program to open out the O. I didn't push my luck with the P. On the cast cover on the fullsize engine the P is solid – so I can argue I'm sticking to prototype.

I'm pretty impressed with my CNC mill; it's by no means new and has been worked fairly hard yet it seemed to be happy with a small cutter where every tenth counts.

Tomorrow I'll see if I can salvage the original cover plate, or whether I'm going to have to make and profile another blank.

Andrew

[JasonBModerator @jasonb]

Andrew, what was the total depth that you had to remove? and any specific reason for using the shallow ap and large ae over a path that used more of the cutters side but with smaller step over?

[DiogenesIIParticipant @diogenesii]

Just got home to ask the same question as JB…?

[Author]

Posts