Holdfast Vacum System?

[paulkane1]

I would appreciate,if anyone on this Forum could help me out on this matter?
I have a Jet 1440 VS Lathe,(M33x3.5mm ),I am in the process of buying the HoldFast Vacum System,which uses a 3/8 inch lamp rod ,which comes through your headstock,( like a knockout bar),and you set up your system,from there.I was checking the Jet knockout for diameter,and it's about 9.5 mm,there still seemed to be a small bit of play as I was pushing through the bar ,in the stock head ,is 3/8 of a inch = to 9.5 mm?Ifb anyone has a Jet 1440 VS Lathe,and are using the HoldFast Vacum System,could you let me know,if ,setting it up ,there was no problems.

Yours Kindly Paul

 

[Duncan A]

Perhaps you should ask Holdfast exactly what the diameter of their tube is? The stated 3/8" may be nominal. Similarly ask Brimarc the exact diameter of the Jet, thus eliminating errors there as well.
For reference, 3/8" is 9.52mm.
Duncan

 

[paulkane1]

Thanks for your replye, The HoldFast system is a American Product,so it's 3/8 of a inch diameter,

 

[finneyb]

Try the US woodturning sites - they have Jet 1440 over there. eg American Woodturning Ass forum https://www.woodturner.org/page/AAWMemberForum or Sawmillcreek


Brian

 

[Hobbyshop]

I happen to have the holdfast on my desk in front of me, and measuring the outside diameter of the threads gives 9.9 mm.
I suggest you confirm you can at least get a 10mm drill into the bore of the headstock, with some clearance.

 

[sunnybob]

you might get help from a UK supplier
https://www.oliverswoodturning.co.uk/pr ... um-system/

 

[paulkane1]

I happen to have the holdfast on my desk in front of me, and measuring the outside diameter of the threads gives 9.9 mm.
I suggest you confirm you can at least get a 10mm drill into the bore of the headstock, with some clearance.

Thanks Kevin for your replye,The spec says ,"suitable for any lathe that has a 3/8 inch or 10 mm hollow bore through the head stock" The Jet spec says,"10mm bore,through head stock"I've got a feeling,there's not going to be much play,if I was to get the rod through,(I'll check later with a 10mm bit),Is the rod made of brass or steel?Would it be possible to burnish of the threads from the rod,( except the threads,at the front of the spindle,and,at the back of the head stock)?if would give a bit of extra play ,were rod rests inside the head stock bore?

 

[Hobbyshop]

Hi Paul

The rod appears to be brass, but you don't need any extra clearance inside the bore, as long as it can be inserted and removed without difficulty.
The rod rotates with the headstock spindle, so there is no relative movement between the brass rod and the inside of the spindle.
The only part of the assembly that remains stationary is the nipple that connects to the vacuum system.

Hope this helps.

 

[Lazurus]

http://www.awgb.co.uk/awgbforum/index.p ... l#msg44330

I made my own to suit the vb36 works a treat.

 

[paulkane1]

Hi Paul

The rod appears to be brass, but you don't need any extra clearance inside the bore, as long as it can be inserted and removed without difficulty.
The rod rotates with the headstock spindle, so there is no relative movement between the brass rod and the inside of the spindle.
The only part of the assembly that remains stationary is the nipple that connects to the vacuum system.

Hope this helps.

Thanks for your help,I just ordered the Holdfast System ,it came this morning,I've set it up ,and, testing it on various size of blanks,I've only the 3 inch ,size chuck,it does not seem to be holding the blanks real solid rigid,I've a 7 bar,30 liter compressor,I think it's giving me enough PSI,I would like to see more grip on the blanks,to ,give me confidence,Would the 6 inch chuck,give me grip ,on the bigger blanks?Are you happy with the amount of grip,on,your Holdfast system?Im only learning vacum chucking,is there any material ,that,you can put on the chuck,or,blank,that would give you extra griping power? Any help would be appreciated.

Paul

 

[finneyb]

Have a look at this http://www.aawforum.org/community/index ... ful.10445/
Your 30 litres/min equates to 1 cfm (cubic ft/min)and that may be the problem.

Brian

 

[paulkane1]

Thanks for your replye,Would you mind clarifying,for my sake,how my 30 litre tank on my compressor is causing the weak grip on my blanks,and,how do I resolve it?

 

[finneyb]

I was reading a 30 litre tank as 30 litres per min flow through the open port.
From the AAW thread It seems, and I have heard it before, that the flow ie litres/min or cfm is important and not just the pressure.

30 litres/min flow is about 1 cfm which seems low if you look at the AAW thread.

HTH

Brian

 

[Hobbyshop]

Hi Paul
The reason I had the adaptor on my desk and could measure it for you was that I have only just purchased it, and was waiting for some vacuum tubing to connect it up.
I have connected it up now and got a good vacuum using a vacuum pump, but I have not actually tested it by turning anything yet.

It sounds like you also purchased the Holdfast vacuum generator, rather than using a pump as I do.
A report I read on the vacuum generator indicated it required a compressor with a minimum capacity of 2 cfm. You don't say what the capacity of your compressor is. The vacuum generator is a venturi system and cannot pull out air at a faster rate than the flow input from the compressor. So effectiveness will depend on leakage rates and this can be affected by the porosity of the wood you are using. You could perhaps try your system with some different species to see if there is any difference.
Take a look at the video here: https://www.youtube.com/watch?v=RQ0CUDzHmd4
It gives information on suitable compressor capacities and the minimum level of vacuum you should consider turning with.

What vacuum are you achieving with your setup? This will be shown on the gauge on the vacuum generator.

There are two things which will affect the holding force on the lathe.
One is the amount of vacuum you can generate - this will determine the pressure difference in psi that will be acting on the outside of the bowl.
As a very rough approximation you can estimate 0.5psi of holding force for each in HG vacuum. So if you are getting the minimum 12" Hg the video recommends then the 3" chuck should give a holding force of approx 42 lbs. (Depends on the actual ID of the 3" chuck, but I am assuming the nominal diameter in the absence of the actual information.)

The other factor is the area of the chuck that the bowl is held against.
In approximate terms the 3" chuck will have an internal area of approx 7 square ins and the 6" chuck will have an area of approx 28 square inches (using nominal diameters rather than actual diameters).
So the 6" chuck will generate 4 times the holding force of the 3" chuck for the same level of vacuum.
However, you will not be able to mount smaller items on the 6" chuck.

And of course, these systems are only ever intended for final finishing cuts, and are not recommended for heavier cuts.

 

[paulkane1]

Thanks Kevin for your reply,My compressor is a 30/15 S Prime Cleanair Brand,7 Bar ,2 HP,with a 30 Ltr Tank,Iy says on info plate,250LT/min ,air displacement,there's no CFM info,so I can't answer anything on that point.At the minute ,I only have the 3 inch chuck,once I get the bigger chucks ,I'll see if there is more grip ,on the big platter blanks?I see you use a air vacum pump ,instead of a compressor,is that right,With a vacum pump,do you not need the Holdfast Generator?Are Vacum Pumps expensive?where would you get a good pump,at a fair price,what about a refurbished one?if you have any links for Vacum pump could you send me it please.

 

[paulkane1]

This is the reading on my Holdfast Generator Guage,Is that a good read,for Vacum Chucking?

.

 

[Phil Pascoe]

This? -
http://www.mgfcompressors.com/products/ ... 5-prime-m/

 

[paulkane1]

Looks like my model

 

[Hobbyshop]

Your compressor is plenty big enough, and the vacuum reading is excellent.
You are unlikely to get much better, whichever system you use.

The bigger chuck will be of benefit with bigger bowls etc., but light finishing cuts are the order of the day whichever chuck you use.
It is also prudent to keep the tailstock in place for as long as you can, only removing it for final finishing of the centre of the foot, and for sanding and polishing.