PDA

View Full Version : Buying Parallel Sets(?)



Smokedaddy
08-15-2005, 03:20 PM
Damn,

Really don’t want to ask this question (fear of coming on as an idiot) but I simply don’t understand. What sort of accuracy would the typical “home shop” machinist need as far as buying a set of parallels? For example, in the latest Travers catalog on page 66 I see a set of parallels advertised as follows (unless they made a typo):

Below is the heading for the add:

------------------------
Accuracy: +-.0003”
------------------------


Then they list the brands:


TTC brand are:
Parallelism in height: +-.0002” to size in height
$49.99


Accurate Accessories brand are:
Parallelism in height: +- 0005” to size in height
$179,29


Would someone mind explaining what this means to a novice. Aren’t the TCC more accurate than the Accurate Accessories brand?

-SD:

[This message has been edited by Smokedaddy (edited 08-15-2005).]

MechHead
08-15-2005, 03:53 PM
We'll assume that the parallels are 1" high;

What they are telling you is that the TTC brand range from .9997 to 1.0003", and the accurate accessories models run from .9995 to 1.0005". The "window" on the TTC units is .0006"; and .001 for the AA model. Given that the AA models have a sloppier tolerance and are almost 4X the price, I would go with the TTC.

Smokedaddy
08-15-2005, 04:42 PM
Me again,

Here's another example from MSC. Aren't the USA ones below (the first ones listed) "more accurate" for a lot less greenbacks? What am I missing?


Brand: USA
Description Standard: Parallel Sets Height Range: 3/4 - 1-3/4 Parallelism: ±0.0001 In. Number of Pieces: 9 Pair
Manufacturer Part Number: 98-410-4
Height Range: 3/4 - 1-3/4 Height (Inch) 3/4, 7/8, 1, 1-1/8, 1-1/4, 1-3/8, 1-1/2, 1-5/8, 1-3/4
Thickness(Inch): ¼
Length (Inch): 6
Parallelism (Decimal Inch): ±0.0001"
Number of Pieces: 9 Pair
Hardness: Rockwell C50-54
Price: $126.00

------------

Brand: B&S
Description: 1/4 In., 9 Pair Parallel Sets Height Range: 3/4 - 1-3/4 x 1/8 Parallelism: ±0.0002 In. Number of Pieces: 9 Pair
Manufacturer Part Number: 599-921-4
Height Range: 3/4 - 1-3/4 x 1/8 Height (Inch) 3/4, 7/8, 1, 1-1/8, 1-1/4, 1-3/8, 1-1/2, 1-5/8, 1-3/4
Thickness (Inch): ¼
Length (Inch): 6
Parallelism: (Decimal Inch) ±0.0002"
Number of Pieces: 9 Pair
Hardness 52-58 HRC
$262.00

-SD:

[This message has been edited by Smokedaddy (edited 08-16-2005).]

Al Messer
08-15-2005, 04:49 PM
I cheat! For what little use I have for parallels, I use ground HSS tool bit blanks stacked up under the work pieces.

jburstein
08-15-2005, 05:27 PM
well for the second pair the cheaper ones are probably not hardened (they don't give a hardness value). Not sure why they aren't as I don't know what good unhardened parallels are, besides maybe being cheap. Plus I thought it was easier to grind hardened steels anyway?

-Justin

[This message has been edited by jburstein (edited 08-15-2005).]

QSIMDO
08-15-2005, 05:49 PM
<font face="Verdana, Arial" size="2">Originally posted by Al Messer:
I cheat! For what little use I have for parallels, I use ground HSS tool bit blanks stacked up under the work pieces.</font>

So...what ARE they used for anyway?

Paul Alciatore
08-15-2005, 06:17 PM
Parallels are used in setups to provide necessary spacing. And other purposes, I am sure. How accurate they need to be depends on the job. For the most part in most setups, the exact dimension is not of great concern. What is more crucial is the consistency of each individual parallel and the match between them.

Consider what is perhaps the most common use. You have a small part to be mounted on the mill, drill press, or some other machine. It is too small for direct clamping so you want to use a vise. But holes need to be drilled through the part and you don't want to make holes in your nice vise. So you use parallels to set it above the bed of the vise. Now, you want the holes to be square so it must be the same amount above at all points. Hence, you need parallels. Matched parallels.

How much error does a difference of 0.001" or 0.0001" make? It depends on the size of the part. For a one inch part, a 0.001" difference between the two parallels would produce a 0.057 degree error (3' 26.26"). Not a lot. For a 0.0001" error, the same 1" part would have about 1/10 that angular error or 0.0057 degree (20.62" - that's seconds). I get a reading of 0.0002" from an oil film on my micrometer. I doubt that many here are carefull enough to insure that the oil film left on their table, vise, parallels, or part is consistently wiped off to those kind of tolerances.

IMHO, 0.0005" tolerance is pleanty good enough for 99.44% of my work. if I really need better, I will probably not be using parallels anyway.

In some cases, you may have to stack the parallels for additional space. Now, the tolerances can add up and increase. So that may also need to be taken into consideration. And of course, the accuracy of the table and the vise and everything else in the setup.

Parallel sets are nice but I have not purchased any. One thing that I see is that they only have two of each size and they are so big. Instead I buy 3' lengths of flat ground stock and slice and dice to get the spacers I want. I can make an assortment of different sizes that will all have the same dimensions, usually well within +/-0.0005". In one setup that I use often, I needed more than one length of ground stock could provide so I bought two. They were about 0.0007" diffrerent, which is fine for most work. But I marked the pieces from each with one and two file notches respectively so I could get a better match when I needed it. A lot cheaper than 10 sets of parallels and I have the sizes I need.

Paul A.

wdglide
08-15-2005, 07:07 PM
<font face="Verdana, Arial" size="2">Originally posted by Paul Alciatore:
Instead I buy 3' lengths of flat ground stock and slice and dice to get the spacers I want.</font>
New guy (first post).

If I were to to the same as you, which stock would I use:
http://www.onlinemetals.com/merchant.cfm?id=268&step=2

wierdscience
08-15-2005, 07:11 PM
Well the Chiwan sets I use are good enough for anything the typical b-port mill is capable of.I got two sets from JTS,cost me $29.95 per set,they checked out parralel within .0002" good enough.

The B&S set may well be import,as will Fowler and several other former"quality" brands.

Smokedaddy
08-16-2005, 12:05 PM
<font face="Verdana, Arial" size="2">Originally posted by jburstein:
...... well for the second pair the cheaper ones are probably not hardened (they don't give a hardness value) ......
</font>

I contacted MSC via email and they said they were Rockwell C50-54.

-SD:

Paul Alciatore
08-16-2005, 05:26 PM
<font face="Verdana, Arial" size="2">Originally posted by wdglide:

Originally posted by Paul Alciatore:
Instead I buy 3' lengths of flat ground stock and slice and dice to get the spacers I want.</font>
New guy (first post).

If I were to to the same as you, which stock would I use:
http://www.onlinemetals.com/merchant.cfm?id=268&step=2



You could use any of the ones described as "precision flat ground stock". I suspect that they are going to be similar in trems of accuracy. The differences would only be of interest if you were going to heat treat them, which I would not recommend for use as parallels unless you intedned to do a finish grinding after.

Paul A.

SGW
08-16-2005, 06:49 PM
FWIW, I got a set of the Travers 1/8" thick parallels a year or two ago. Matched and parallel to within a few tenths, as best I can measure. The set I got came in a pretty decent molded plastic case. The set of 10 (8?) pairs was on sale for $29.95 or something. I thought and still think it was a heck of a bargain.

3 Phase Lightbulb
08-16-2005, 06:58 PM
IMHO, It doesn't matter how good your parallel set is. If your vise is not square/tramed to your head, a bad parallel set might even give you more squareness than a perfect set http://bbs.homeshopmachinist.net//smile.gif Buy a cheap set of parallels, and buy a high quality vise and a high quality dial indicator.

-Adrian

QSIMDO
08-16-2005, 06:58 PM
Thanks Paul, et al.

How 'bout that; you taught, I learned...hell of a day so far I'd say!

John Stevenson
08-16-2005, 07:19 PM
I'll go with Paul A on this one and use Ground Flat Stock [ GFS ].

As Paul says it's probably better than we can work to and most of the equipment that we have access to IF we are honest.

One drawback to advertised ones seems to be the fact that they are not hardened but in fact used carefully this is a plus.
If you do make a mistake and wing a home made parallel or drill thu you will have a witness mark, so what, when you get 80 dings in it throw it away and get a new one http://bbs.homeshopmachinist.net//biggrin.gif

With the commercial hardened ones one slip and it's the tool gone.
Another drawback to commercial ones is that they make these bang on commercial sizes like 1/4" and 1/8" etc.
If you want to hold a piece of 1/4" stock in the vise one 1/4" parallel will nip at the same time the stock does but often first if the jaws are splayed with the result that the job isn't held tight.
Two 1/8" have the same effect and one 1/8" can cause rocking.

Because we have a good choice of imperial and metric GFS in the UK I tend to buy Metric sizes as in 1mm increments that's only 40 thou under and you get a far greater choice.

Choice of sizes is also important and not addressed by the commercial sets as they have no idea to what use they are needed.
If you have a vise with 1-1/2" tall jaws then anything over 1-3/8" is wasted. That nice 9 piece set is now down to 6 piece.

It does pay to mix and match with off the shelf GFS pieces. Carefull use and a bit of a hone with a stone every now and again will ensure that these soft pieces will still last.

Sir John .

Smokedaddy
08-17-2005, 02:17 AM
Thanks for the responses and different ideas but I'd still like to know if I'm screwed up from my original posting? Aren't the less expensive ones more accurate, like the $126.00 ones?

-SD:

Paul Alciatore
08-17-2005, 03:24 AM
<font face="Verdana, Arial" size="2">Originally posted by Smokedaddy:
Thanks for the responses and different ideas but I'd still like to know if I'm screwed up from my original posting? Aren't the less expensive ones more accurate, like the $126.00 ones?

-SD:
</font>

Smoke,

That's a hard one to answer and that is likely why it wasn't answered. You would expect / hope that the more expensive tools would be worth the extra expense. But the differences may not be in just the accuracy. The more expensive sets may have more sizes. Or a nicer surface finish. Or a nicer case. They may come with certificates of accuracy or be traceable to the NBS. Some companies have better service after the sale.

Another difference could be the country of origin. Lets face it, items made in the USA will be more expensive than those made in the Pacific rim. Are they always better? No, not always.

Unless you can find someone who has purchased all the various brands you mention or can find a store that stocks them all where you can inspect them, I doubt that you will ever know for sure.

I know that does not fully answer your question but it's the best I can do.

One further comment on John S's comment. He says that unhardened parallels may actually be better. I have to agree because if you accidentally drill or cut into them, they will not dull or break your tool as easily as a hardened one would. And that happens in the best of shops.

Paul A.

madman
08-17-2005, 11:49 AM
Buy the cheapest ones you can. Unless youre machining to bizarre tolerances the cheapies will suffice and serve you well. Buy a set of thin ones and a set of thick ones. When you acidentally drill a hole through them later on having the cheap ones wont hurt as much. (or when your best buddy comes over and drills into them looks at you and says sorry you can tell him oh no those were the most expensive parallels i could buy and make some money of the twit. ) Revenge is sweet.

Smokedaddy
08-17-2005, 01:58 PM
Okay ... thanks, but if you re-read the THIRD posting, the less expensive ones are made in the USA. The only differences in my listing are:

Parallelism (Decimal Inch): ±0.0001"
Hardness: Rockwell C50-54
Price: $126.00

---

Parallelism: (Decimal Inch) ±0.0002"
Hardness 52-58 HRC
$262.00

-SD:

[This message has been edited by Smokedaddy (edited 08-17-2005).]