Bridgeport M head performance

Hello I would like to know if anyone out there can help me understand a little more regarding the performance of A Bridgeport M head,,, I recently purchased one from me friend whose father owned it who actually was the original owner ,, it has the standard 1/2 hp motor that came with it back in 1940 I believe and the machine is in wonderful condition hardly any backlash at all everything tight and beautifully taken care of,,, The maximum end mill size is 1/2 inch And when I throw in a brand new 4 fluted end mill it seems I can only take very small minimal cuts with it like 1/16” at a time,, any more than that and the machine just bogs down and eventually comes to a stop .. my travel speed is very slow and it just seems that it should be able to do you a little better than that ,,, I just have to slowly nibble away at whatever I’m cutting which was aluminum and some brass,,, I can imagine if I were cutting some much harder material like stainless steel or something ,,,is this What’s to be expected with this machine and it’s 1/2 horse power motor..?
I know this is the first machine Bridgeport came out with and all the others seem to have gotten more powerful as the years have going on is this what I can expect as far as any work I plan on doing with it ,, just take a very small little cuts and work my way through it without going too deep while traveling very slowly,,, I took the motor in thinking that it might be worn out but they told me the motor is working fine and I had them put new bearings in it anyways ..I thought the belt might be slipping Explaining why it would slowly slow down and come to a stop but i’ve locked it down as tight as it will go and the belt seems like it’s tight enough .. The machine also came with a VFD which converted it to single phase power .. I don’t know much about the operation on that other than just speeding it up or slowing it down but when I looked up the manual online there was a category that talked about torque and I was wondering if that meant that the torque of the motor can be adjusted also thinking that maybe that’s why it’s not cutting through and bogging down to a stop ..???
Anyway I’m very new to this stuff and I know there are professionals out there that know much more about these machines and any help on the matter would be greatly appreciated thank you ..

How deep are you cutting? If the whole side of the end-mill is engaged in the work, then you won't be able to do more than a light clean-up pass.

It sounds like you've covered most everything else. They are a light duty machine by design.

I wonder if the VFD is mis-programmed or you have not picked the optimum belt speed setting. Years ago, I had a Clauseport, which was a like-new Clausing 8520 body with a Bridgeport M head I spliced on. It was no 40-taper VMC, for sure, but could take an OK-enough cut that I would be more limited by the machine's rigidity and the cleanup associated with throwing chips all over, rather than a particular lack of grunt.