Thread: UP CUT..DOWN CUT

You didn't say whether you were cutting metal or timber,assuming you are cutting timber products I'll try to help ,I cut a lot of MDF,with variable results,naturally.
If you can indicate what you want to cut,no doubt there will be plenty of people,me included that can help,its a pretty large subject,but there are some very knowledgeable people who can advise you.

Originally Posted by broomy

You didn't say whether you were cutting metal or timber,assuming you are cutting timber products I'll try to help ,I cut a lot of MDF,with variable results,naturally.
If you can indicate what you want to cut,no doubt there will be plenty of people,me included that can help,its a pretty large subject,but there are some very knowledgeable people who can advise you.

Hi Broomy, sorry in my haste I forgot to say that it mainly wood that I will be carving, e.g pine mdf etc

Nick

MDF is IMO heavy cardboard,it varies from suppliers,I have had some real rubbish,so upcut/downcut won't make a lot of difference to that type of MDF,it appears that the lighter the colour the harder to get a clean,unfurry,non clogging tool of ANY type,and I've used a lot.Judging the density takes time,mine comes from Sydney thru'a local Cabinet maker so you get what turns up.
Essentially tools should clear up or down,altho' if a downcutter is working on a waste board its a mystery to me where the scarf is supposed to go.
Any'ow up/down,single flute,double flute all perform,---as long as they're sharp and spindle and axis speeds are OK.
The main thing is having sharp tools. I went for years trusting a local saw sharpener,with sometimes bad results,blaming everything but them.
I use Melbourne company,Carb i Tool, ATM trying 6mm spiral upcutter,good result[also good MDF],resharpening costs there are very reasonable 1/3 third the price of my local cowboys.They also post things not use a expensive courier.
They have a Tech wallah who is very helpful even if like me you are small fry!

There are basically three families of solid solid carbide spiral bits, up spiral, down spiral, and compression.

Up spiral have the spiral arranged similar to a twist drill, so that the bit rotation tends to draw the swarf up and out of the cut for collection. The downside is that this also tends to raise the adjoining surface and cause surface breakout and chipping. Ideal for mortising etc where swarf removal is more critical than surface finish.

Down spiral have a reverse spiral which tends to push the swarf back into the cut. As such they tend to clog the cut path with dust, and it is harder to draw it out. However the down force from the cut acts against the surface pushing it toward the tip of the bit so it is backed up by the material below, virtually totally eliminating surface breakout in most materials. (May not help for short grain brittle materials like the surface veneer of some cheap plywoods which are not really suitabale for routing.) If you are making multiple cuts side by side, dust extraction is much easier after the first pass as the subsequent passes remove at least one wall making the swarf more more accessible.

Compression bits have an up cut at the tip, and transition to a down cut in the middle of the material. This effectively ensures that the shear force at each surface is inwards and all surfaces are backed up by the core of the material. This family are primarily used for cutting out components from sheet goods, including melamine coated chipboard and MDF where there is very low tolerance for surface chipping etc. They are generally made for specific material thickness ranges, as this controls where the transition from up to down occurs. If used for shallow routing (transition above the surface) they function as upcut bits. Dust extraction can be an issue as they combine the extraction issues of a downcut bit at the top surface with the restriction at the transition point.

Originally Posted by malb

There are basically three families of solid solid carbide spiral bits, up spiral, down spiral, and compression.

Up spiral have the spiral arranged similar to a twist drill, so that the bit rotation tends to draw the swarf up and out of the cut for collection. The downside is that this also tends to raise the adjoining surface and cause surface breakout and chipping. Ideal for mortising etc where swarf removal is more critical than surface finish.

Down spiral have a reverse spiral which tends to push the swarf back into the cut. As such they tend to clog the cut path with dust, and it is harder to draw it out. However the down force from the cut acts against the surface pushing it toward the tip of the bit so it is backed up by the material below, virtually totally eliminating surface breakout in most materials. (May not help for short grain brittle materials like the surface veneer of some cheap plywoods which are not really suitabale for routing.) If you are making multiple cuts side by side, dust extraction is much easier after the first pass as the subsequent passes remove at least one wall making the swarf more more accessible.

Compression bits have an up cut at the tip, and transition to a down cut in the middle of the material. This effectively ensures that the shear force at each surface is inwards and all surfaces are backed up by the core of the material. This family are primarily used for cutting out components from sheet goods, including melamine coated chipboard and MDF where there is very low tolerance for surface chipping etc. They are generally made for specific material thickness ranges, as this controls where the transition from up to down occurs. If used for shallow routing (transition above the surface) they function as upcut bits. Dust extraction can be an issue as they combine the extraction issues of a downcut bit at the top surface with the restriction at the transition point.

Thanks for the info Malb, very clear, at least I will now know what to look for when buying end mills.

Nick

Originally Posted by broomy

MDF is IMO heavy cardboard,it varies from suppliers,I have had some real rubbish,so upcut/downcut won't make a lot of difference to that type of MDF,it appears that the lighter the colour the harder to get a clean,unfurry,non clogging tool of ANY type,and I've used a lot.Judging the density takes time,mine comes from Sydney thru'a local Cabinet maker so you get what turns up.
Essentially tools should clear up or down,altho' if a downcutter is working on a waste board its a mystery to me where the scarf is supposed to go.
Any'ow up/down,single flute,double flute all perform,---as long as they're sharp and spindle and axis speeds are OK.
The main thing is having sharp tools. I went for years trusting a local saw sharpener,with sometimes bad results,blaming everything but them.
I use Melbourne company,Carb i Tool, ATM trying 6mm spiral upcutter,good result[also good MDF],resharpening costs there are very reasonable 1/3 third the price of my local cowboys.They also post things not use a expensive courier.
They have a Tech wallah who is very helpful even if like me you are small fry!

Thanks Broomy, I will have to shop around now and at least I will know what to look for.

Nick