OXA toolpost on the HobbyMat MD65 lathe

[Dinsen]

My wife was so kind to give me a Drillpro 250 OXA-type toolpost for my lathe for Christmas I thought I'd share my experience adapting and using it on my HobbyMat MD65 lathe in this thread as a review. This lathe is also known as the Prazimat SD300.

These toolposts are available from several sellers. I helped my wife getting it from Banggood. There are plenty of reviews of the toolpost itself on BG, so I'll not dive furhter into that, but focus on fitting it on the HobbyMat since it's not that straight forward.



This picture here shows the toolpost mounted on the compound slide. This is how I have it now, and what I'll be testing initially. Note that the tool holder itself is offset off the top face of the compound slide. I'm using an 8mm insert tool here, and it needs to be raised 1.0mm with a spacer when fitted directly in the original inverted-tophat tool holder. But since the Drillpro toolpost comes with holders that are several mm thick they have to sit off the side of the slide. The issue is down to the vertical compactness of the lathe, which is great for precision but creats a pain here.

But let's summarize some measurements firs:

The toolpost has a 10 mm bolt hole in the middle. The handle turns around that and it's fitted with a big nut on the top through a threaded rod. The threaded rod is included with the kit.

The compound slide has three mounting holes, two of which can be seen in the picture below. They are used to bolt on the original inverted-tophat holder. (I've never needed the third one, but I think it accomodates a vise when the compound slide is used vertically on the milling attachment. It is blanked off with a screw.) All three are M8 threaded.

The leftmost bolt hole is about 20mm from the edge of the slide - almost exactly the same as the face of toolpost. The second is further 20mm from the first hole.

Using the leftmost hole, this was my first crude attempt at fitting:



I cut down the M10 threaded rod included with the kit to have an M8 thread in the end, but I screwed up, and ended up with a twisted M8 thread, so the rod is now in my scrap-box.

I then took a new piece of M8 threaded rod and turned a 10mm aluminium busihing. Looks rather nice, doesn't it?



It was'nt!

The 20 distance to the edge is *almost* the same, but not *exactly* the same as the distance from the centre of the through hole in the toolpost to the left face of it. If you look closely in the picture above with the long M8 bolt through the toolpost, you can see it doesn't align with the middle of the QCTP when the tool holders are off the edge of the slide.

This was my crisis moment.

And I took a long walk with my wife and our dog...

After all, it's Christmas time. Time to calm down and enjoy family life....

But my mind kept working.

And while walking, it dawned that I had a good piece of 10mm diameter mild steel rod. What if I made a new threaded rod out of it with an M10 thread in one end of the top not, and an M8 thread in the other, but with the M8 stud eccentric on the rod?!

I have not yet received the independent 4-chuck which I have been working on, so I had to find a spacer-piece for my 3-chuck. From my calculations, this needed to be 1.49mm. I found a spacer which was 1.44, and started turning. Eventually, I had this:



And after some careful (very careful!) threading, I eventually had a useful, but strange 10mm rod fitted on the slide:



Let me explain: The idea is that by turning the rod a quarter turn, I can offset the toolpost exactly where I want it on the top slide, as shown in the first picture.

Testing it, I've identified at least five potential problems with this solution:

1. What about the other side of the toolpost - the boring side (sic!), you may ask. Well, fortunately my boring tools have small 6mm diameter rods so they do actually fit on the toolpost even though they can't fit off the side of the slide.
2. I can't angle the tools as the tool holders are fixed to sit perpendicularly on the top slide due to the fitting off the slide. This becomes a problem when turning tapers.
3. The top nut should never be tightened strongly or the M8 thread will crack the cast iron slide. The fact that the fitting stud is eccentric only makes matters worse as the tension is not perfectly perpendicular to the slide surface! The original tool holder has two bolt holes and they are known to crack the slide when overtightened.
4. The top surface on the compound slide and the bottom surface on the OXA QCTP are smooth and it rotates easliy around it's axis when tools are tightened.
5. This leads also to another drawback: When I used it for boring, the toolpost did actually rotate without me noticing it causing the bore to end up being tapered.

Searching for sutable toolposts, I found an alternative to the OXA tool post which will rectify some (but not all) of the above issues as it is designed for the HobbyMat and therefore bolted on the compound slide through both holes. I thought a lot about that but ended up not putting in on my wish list due to its price and since I want to be able to use the toolpost directly on the cross slide, which the OXA post will accomodate. And I can still revert back to the original tool holder.

And despite the problems, I'm a happy HobbyMat owner, now with a nice QCTP

I'll now start working on an adapter plate for fitting the QCTP on the cross slide. Stay tuned, as they say

 

[Firstram]

Flip your tools over and run the lathe in reverse!

 

[Dinsen]

Flip your tools over and run the lathe in reverse!

 

[RaisedByWolves]

My wife was so kind to give me a Drillpro 250 OXA-type toolpost for my lathe for Christmas I thought I'd share my experience adapting and using it on my HobbyMat MD65 lathe in this thread as a review. This lathe is also known as the Prazimat SD300.

These toolposts are available from several sellers. I helped my wife getting it from Banggood. There are plenty of reviews of the toolpost itself on BG, so I'll not dive furhter into that, but focus on fitting it on the HobbyMat since it's not that straight forward.

View attachment 515447

This picture here shows the toolpost mounted on the compound slide. This is how I have it now, and what I'll be testing initially. Note that the tool holder itself is offset off the top face of the compound slide. I'm using an 8mm insert tool here, and it needs to be raised 1.0mm with a spacer when fitted directly in the original inverted-tophat tool holder. But since the Drillpro toolpost comes with holders that are several mm thick they have to sit off the side of the slide. The issue is down to the vertical compactness of the lathe, which is great for precision but creats a pain here.

But let's summarize some measurements firs:

The toolpost has a 10 mm bolt hole in the middle. The handle turns around that and it's fitted with a big nut on the top through a threaded rod. The threaded rod is included with the kit.

The compound slide has three mounting holes, two of which can be seen in the picture below. They are used to bolt on the original inverted-tophat holder. (I've never needed the third one, but I think it accomodates a vise when the compound slide is used vertically on the milling attachment. It is blanked off with a screw.) All three are M8 threaded.

The leftmost bolt hole is about 20mm from the edge of the slide - almost exactly the same as the face of toolpost. The second is further 20mm from the first hole.

Using the leftmost hole, this was my first crude attempt at fitting:

View attachment 515451

I cut down the M10 threaded rod included with the kit to have an M8 thread in the end, but I screwed up, and ended up with a twisted M8 thread, so the rod is now in my scrap-box.

I then took a new piece of M8 threaded rod and turned a 10mm aluminium busihing. Looks rather nice, doesn't it?

View attachment 515450

It was'nt!

The 20 distance to the edge is *almost* the same, but not *exactly* the same as the distance from the centre of the through hole in the toolpost to the left face of it. If you look closely in the picture above with the long M8 bolt through the toolpost, you can see it doesn't align with the middle of the QCTP when the tool holders are off the edge of the slide.

This was my crisis moment.

And I took a long walk with my wife and our dog...

After all, it's Christmas time. Time to calm down and enjoy family life....

But my mind kept working.

And while walking, it dawned that I had a good piece of 10mm diameter mild steel rod. What if I made a new threaded rod out of it with an M10 thread in one end of the top not, and an M8 thread in the other, but with the M8 stud eccentric on the rod?!

I have not yet received the independent 4-chuck which I have been working on, so I had to find a spacer-piece for my 3-chuck. From my calculations, this needed to be 1.49mm. I found a spacer which was 1.44, and started turning. Eventually, I had this:

View attachment 515452

And after some careful (very careful!) threading, I eventually had a useful, but strange 10mm rod fitted on the slide:

View attachment 515453

Let me explain: The idea is that by turning the rod a quarter turn, I can offset the toolpost exactly where I want it on the top slide, as shown in the first picture.

Testing it, I've identified at least five potential problems with this solution:

1. What about the other side of the toolpost - the boring side (sic!), you may ask. Well, fortunately my boring tools have small 6mm diameter rods so they do actually fit on the toolpost even though they can't fit off the side of the slide.
2. I can't angle the tools as the tool holders are fixed to sit perpendicularly on the top slide due to the fitting off the slide. This becomes a problem when turning tapers.
3. The top nut should never be tightened strongly or the M8 thread will crack the cast iron slide. The fact that the fitting stud is eccentric only makes matters worse as the tension is not perfectly perpendicular to the slide surface! The original tool holder has two bolt holes and they are known to crack the slide when overtightened.
4. The top surface on the compound slide and the bottom surface on the OXA QCTP are smooth and it rotates easliy around it's axis when tools are tightened.
5. This leads also to another drawback: When I used it for boring, the toolpost did actually rotate without me noticing it causing the bore to end up being tapered.

Searching for sutable toolposts, I found an alternative to the OXA tool post which will rectify some (but not all) of the above issues as it is designed for the HobbyMat and therefore bolted on the compound slide through both holes. I thought a lot about that but ended up not putting in on my wish list due to its price and since I want to be able to use the toolpost directly on the cross slide, which the OXA post will accomodate. And I can still revert back to the original tool holder.

And despite the problems, I'm a happy HobbyMat owner, now with a nice QCTP

I'll now start working on an adapter plate for fitting the QCTP on the cross slide. Stay tuned, as they say

Nice writeup!

I know we have discussed this before, but for the sake of those wanting more info, you have several options.

Obviously smaller tooling. This can be difficult to obtain for carbide insert tooling, but HSS toolbits come in very small sizes and will do as good if not better than carbide for most tasks.

You could remove material off of the bottom of the tool holders. I only recommend this as you can get these toolholders for very cheap if you watch BG and Ali for deals. Therefore if something goes wrong or you don't like the end result its no big deal financially.

As to your compound rotating, I've seen a paper disk suggested to add a little friction between the tool post and top slide, but for me I used a little lapping compound. Just a tiny bit applied with a tooth pick and dabbed around with my finger. This will add some roughness to the two smooth surfaces and can be removed entirely after a period of use if there are concerns of it getting in where it shouldn't.

Food for thought.

 

[Dinsen]

Nice writeup!

I know we have discussed this before, but for the sake of those wanting more info, you have several options.

Obviously smaller tooling. This can be difficult to obtain for carbide insert tooling, but HSS toolbits come in very small sizes and will do as good if not better than carbide for most tasks.

You could remove material off of the bottom of the tool holders. I only recommend this as you can get these toolholders for very cheap if you watch BG and Ali for deals. Therefore if something goes wrong or you don't like the end result its no big deal financially.

As to your compound rotating, I've seen a paper disk suggested to add a little friction between the tool post and top slide, but for me I used a little lapping compound. Just a tiny bit applied with a tooth pick and dabbed around with my finger. This will add some roughness to the two smooth surfaces and can be removed entirely after a period of use if there are concerns of it getting in where it shouldn't.

Food for thought.

Thanks, and yes food for thought, I like that! I really like your idea of using lapping compound, which I don't have, but perhaps some toothpaste will do.

However, I think I solved it: I sanded off the paint on the bottom of the QCTP with fine grit paper and cleaned the upper surface of the compound slide with IPA. That seems to have helped. When i cleaned up my machine from the previous owner's mis-storage of it I used petroleum and lots of oil. The oli is mean that all surfaces are still "slippery" - good for my machine...

Also, my eccentric adjustment bolt really helps when the tools are straight.

It started as a pragmatic solution to an annoying problem, but it has a huge advantage in practice:

Here's what I do: I turn the through-bolt to roughly the right place, fit a tool on the QCTP, and tighten the top nut lightly with a 17-spanner. This adds a little rotation to the through-bolt drawing the tool holder just a slight bit closer to the edge of the slide and I can run the tool perfectly aligned. Releasing the QCTP, the tool slides off the edge and can be removed and a new one fitted wihtout distorting the alignment.

And there's more: This not only keeps everyting straight, it also takes tension off the throghbolt and hence the fitting hole in the top slide. My cracking-anxiety is gone!

I'll be away for a few days, but will then start working on the plate for fitting on the cross slide.